THERMOCHROMIC EFFECT PIGMENT AND PROCESS FOR PRODUCING THE SAME

Abstract: The invention relates to a thermochromic effect pigment comprising a thermochromic liquid crystal material encapsulated with a polymer and coated with one or more inorganic metal oxides or nearly insoluble metal salts selected from Al2O3, SnO2, ZrO2, TiO2, CaO, SiO2, ZnO, MgO or BaSO4. The pigment is stable in solvent-based formulations and can be used as colourant in form of an aqueous suspension or as powder in lacquer compositions, plastic compositions, dyed filter compositions, dyed glass compositions, dyed cosmetic compositions, printing ink compositions, and in hair colouring agents.

Description: Thermochromic Effect Pigment and Process for Producing the Same The .invention relates to a thermochromic effect pigment comprising a thermochromic liquid crystal material encapsu¬ lated with a polymer and coated with one or more inorganic metal oxides or nearly insoluble metal salts. There is a continuously increasing demand for liquid crystal pigment as coating layer onto a substrate or for use in printing, in lacquer formulations, in plastics and cosmetics. At present, for make-up cosmetics such as foundations, eye shadows, cheek rouges and other cosmetics thermochromic effect pigments are desired because of their colour play. EP-A-0 383 376 discloses a liquid crystal pigment consisting of a lamellar particle which is coated with a liquid crystal¬ line material. The pigment is manufactured by dissolving a liquid crystalline material in a suitable solvent, dispersing a lamellar particle in the solvent and coating the lamellar particle by precipitating a portion of the liquid crystalline material from the solution onto the lamellar particle. This pigment has the disadvantage that it is not resistant against solvents, has low mechanical stability and poor flowability. Accordingly, it is object of the present invention to provide thermochromic effect pigments with improved resistance against solvents and good mechanical stability and flowabil¬ ity so that it can be used like a common pigment. Furthermore it is an object of the present invention to modify colour play and colour change in a definite way. This object is accomplished according to the present inven¬ tion by a thermochromic effect pigment comprising an encapsu¬ lated thermochromic liquid crystal which is coated with one or more inorganic metal oxides, mixtures of inorganic metal oxides, or nearly insoluble metal salts. Furthermore this object is accomplished according to the present invention by a process for preparing thermochromic effect pigments by precipitating a metal oxide or metal salt in an aqueous suspension onto the encapsulated liquid crystal in well-known manner. The inorganic metal oxides or metal salts can be selected for example from Al 2 0 3 , Sn0 2 , CaO, Si0 2 , Zr0 2 , Ti0 2Λ ZnO, MgO or BaS0 4 and can be precipitated on to the encapsulated liquid crystal as single oxide or as mixed oxide thereof. The mixed oxide preferably contains silicon dioxide. The amount of metal oxides or salts in the thermochromic effect pigment as a rule is from 2 to 50 %, preferably from 5 to 15 % by weight, relative to total pigment weight. ' The encapsulated thermochromic liquid crystal material is a commercially available material. The liquid crystals are encapsulated by complex coacervation in gelatin and gum arabic (US patent 2800457) , coacervation in gelatin (US patent reissue 24899) , by interfacial- polymerisation in polyester (US patent 3429827) , by interfacial polymerisation in polyamide (US patent 3208951) or other processes well known in the art. The amount of polymer in the encapsulated thermochromic liquid crystal material is from 0.1 to 25 %, preferably 2 to 10 % by weight, relative to total weight of the encapsulated liquid crystal material. A suitable thermochromic liquid crystal material is Lic- ritherm® TCC-1001 consisting of a thermochromic liquid crystal encapsulated with gelatin manufactured by Merck Ltd. The liquid crystal is an admixture of at least three chiral components and optionally at least one non-chiral component. At least one chiral component is a compound of the formulae I or II Ri-(Ai-Zi) m -A2-R* I wherein R 1 is R* or an alkyl radical or an alkenyl radical with up to 18 C atoms optionally substituted by CN or at least one halogen atom, wherein one or two non-adjacent CH 2 groups of this radicals can also be replaced by -0-, -CO-, -O-CO- and/or -C0-0-, A 1 and A 2 are in each case independently of one another a) a 1,4-cyclohexylene group, wherein one or two non- adjacent CH groups can also be replaced by -O- and/or -S- and/or which can be substituted in the 1-position by a CN- or CH 3 -group. -4- b) a 1,4-cyclohexenylene, a piperidine-l,4-diyl or 1,4- bicyclo[2,2,2]octylene group, or c) a 1,4-phenylene group optionally substituted by one or two F-atoms or one or two CN- or one or two CH 3 - groups, wherein at least one CH group can also be replaced by N, Zi is -CO-0-, -0-CO-, -CH 2 CH 2 -, -CHCN-CH 2 -, -CH 2 -CHCN-, CH≡CH-, -0CH 2 -, -CH 2 0-, -CH=N-, -N=CH-, -NO=N, -N=NO- or a single bond, m is 0 r 1, 2 or 3, and R* is a chiral radical imparting optical activity to the compound of the formula I; Ster-0-CO-(Ai-Zi) m -CH 2 -R3 II wherein A 1 , Z 1 and m have the meaning giving for formula I, and R 3 is a normal or branched alkyl or alkenyl radical with up to 16 C atoms wherein one CH 2 group may be replaced by -0-, -O-CO- or -C0-0-, and Ster denotes a saturate or unsaturated gonan-3-yl group being optionally substituted by up to 6 normal or branched alkyl radicals with 1 to 10 C atoms. R* can also be a chiral radical of the formula III -Q-C-R° III I Y wherein is a single bond or an alkylene group with 1-8 C atoms, wherein one or two non-adjacent CH 2 groups can be replaced by -CH(CN)-, -CH(F)-, -CH(C1)-, -0-, -S-, -CO-O- or O-CO X is H or CH 3 Y is F, Cl, Br, CN or CH 3 R° is an alkyl residue being different from X with up to 14 C atoms, wherein one or two non-adjacent CH 2 groups may be replaced by -0-, -CO-O- or -0-CO-. Furthermore at least one non-chiral compound is a compound of the formula IV R2-(A3-Z2) p -A4-Z3-A 5 -R 4 IV R2 and R-x in each case independently of one another are an alkyl radical or an alkenyl radical each with up to 18 C atoms optionally substituted by CN or at least one halogen atom, wherein one or two non-adjacent CH 2 groups of these radicals can also be replaced by -0-, -CO-, -0-CO- and/or -C0-0-, one of R 2 and R 4 may also be CN or halogen, A3, " and A 5 are in each case independently of one another a) a 1,4-cyclohexylene group, wherein one or two non- adjacent CH 2 groups can also be replaced by -0- and/or -S- and/or which can be substituted in the 1-position by a CH 3 - or CN-group, b) a 1,-4-cyclohexenylene, a piperidine-l,4-diyl or 1,4- bicyclo[2,2,2]octylene group, or c) a 1,4-phenylene group optionally substituted by one or two F atoms or one or two CH 3 - or one or two CN groups Z 2 and Z3 are each -C0-0-, -0-C0-, -CH 2 CH 2 -, -CHCH-CH 2 -, -CH 2 -CHCN-, -CH=CH-, -OCH 2 ~, -CH 2 0-, -CH=N-, -N=CH-, -NO=N, -N=NO- or a single bond, and p is 0, 1 or 2. As thermochromic liquid crystal can also be used Licitherm® TCC—216, a mixture of thermochromic liquid crystal compounds with the following composition (manufactured by Merck Ltd.) : The designation TCC means that the mixture has been microen- capsulated according to the process of US-A-2 800 457, exam¬ ple 2. In the above formulation, the compounds listed are as below: CE4 S-(+)-4-(2-methylbutyl)phenyl 4-n-hexy1oxybenzoate CE4R Racemic 4-(2-methylbutyl)phenyl -n-hexy1oxybenzoate CE5 S-(+)-4-(2-methylbutyl)phenyl 4-n-octyloxybenzoate CE6 S-(+)-4-(2-methylbutyl)phenyl 4-n-decyloxybenzoate CE7 S-(+)-4-(2-methylbutyl)phenyl 4-n-dodecyloxybenzoate ME805 4-n-pentylphenyl 4-n-octyloxy- benzoate CE10MBR Racemic 4-(2-methylbutyl)phenyl 4-methoxybenzoate The encapsulated liquid crystal material is suspended in deionized water in a concentration from 3 to 10 % by weight and heated to within the range from room temperature to 100 °C, preferably 70 to 80 °C while stirring. The pH value is adjusted to within the range of the corresponding precipita¬ tion pH value of the metal hydroxide or metal oxide hydrate or the nearly insoluble metal salt according to known methods for the coating of platelet-like substrates. The coating with A1 2 0 3 is described in DE-B-24 29 762 and the coating with Si0 2 in DE-B-21 06 613. DE-B-2 522 573 and EP-B-0 220 509 disclose the coating with Sn0 2 . Finally EP-B-00 82 986 describes the coating with MgO, DE-B-2 009 566 the coating with Ti0 2 , EP-A-0 256 417 the coating with ZnO and EP-A-0 268 918 the coating with ZrO. The precipitation of barium sulfate onto flaky pigments is described in EP-A-142 695. After adjustment of the pH value an aqueous solution of a metal salt is added. The solution pH is maintained substan¬ tially constant by means of a dilute base. Subsequently, the suspension is cooled, sucked off and washed with deionized water and then the coated liquid crystal material is dried for 3 to 10 minutes, preferably 4 to 6 minutes at 90 to 130 °C, preferably 95 to 110 °C. It is also possible to dry the product for a longer period of time (e.g. overnight) at lower temperatures, e.g. 50 to 70 °C. However, it is not necessary to dry the pigment; it may be used in the form of the aqueous final suspension as described above. The product can also be freeze-dried or spray-dried to a powder. The thermochromic effect pigment can be used as colourant in lacquer compositions, plastic compositions, dyed filter compositions, dyed glass compositions, dyed cosmetic composi¬ tions, printing ink compositions, and in hair colouring agents. However, the use of the pigment is not limited to these applications. The pigment according to the present invention has the advan¬ tage that it can be used as powder for the above-mentioned applications. The pigments are stable in solvent-based formulations, as well as in water-born systems. The invention will now be described more specifically with reference to examples thereof which are not intended to limit the scope of the invention. Example 1 25 g encapsulated liquid crystal material (Licritherm® TCC 216), a 33 % aqueous suspension with a dry matter of 8.25 g, is suspended in 750 ml deionized water and heated to 75 °C while stirring. The pH value is adjusted to 7.0 with 5 % NaOH solution. 11.84 g A1C1 3 • 6 H 2 0 in 200 ml water is added to the suspen- sion with a rate of 1.5 ml/min. During the addition of the A1C1 3 solution the pH is maintained at 7.0 by the simultaneous addition of 5 % NaOH solution. Subsequently, the suspension is cooled, sucked off and washed with 15 1 deionized water chloride free and dried for 5 min at 100 °C. Example 2 25 g encapsulated liquid crystal material (Licritherm® TCC-1001) with a solid content of 8.25 g is suspended in 750 ml water. The suspension is heated to 60 °C while stirring and the pH value is adjusted to 9.0 with 5 % NaOH solution. Then 1.67 ml sodium water glass solution (dilution 1:1 with water) in 50 ml water are added. During the addition the pH value is maintained at 9.0 by the simultaneous addition of 10 % hydro- chloric acid. Upon completion the suspension is stirred for 15 minutes. The pH is then lowered to 6.5 and the suspension is stirred for further 15 minutes. 0.49 g A1C1 3 • 6 H 2 0 and 0.29 g Na 2 S0 4 (anhydrous) are added and the suspension heated to 95 °C for 30 minutes. Subse- quently, the suspension is cooled, sucked off, washed and dried over night at 50 °C. Example 3 25 g encapsulated liquid crystal material (Licritherm® TCC—1001) with a solid content of 8.25 g is suspended in 750 ml water. The suspension is heated to 60 °C while stirring and the pH value is adjusted to 9.0 with 5 % NaOH solution. Then 2.24 ml sodium water glass solution (dilution 1:1 with water) in 100 ml water are added. During the addition the pH value is maintained at 9.0 by the simultaneous addition of 10 % hydro¬ chloric acid. Upon completion the suspension is stirred for 15 minutes. Then the suspension is cooled, sucked off, washed and .dried over night at 50 °C. Example 4 25 g encapsulated liquid crystal material (Licritherm® TCC-1001) with a solid content of 8.25 g is suspended in 750 ml water. The suspension is heated to 75 °C while stirring and the pH value is adjusted to 11 with 5 % NaOH solution. Then 2.07 g MgCl 2 • 6 H 2 0 in 100 ml water are added. During the addition the pH value is maintained at 11 by the simultaneous addition of 10 % NaOH solution. Upon completion the suspension is stirred for 15 minutes. Then the suspension is cooled, sucked off, washed and dried over night at 50 °C. Example 5 25 g encapsulated liquid crystal material (Licritherm® TCC-1001) with a solid content of 8.25 g is suspended in 750 ml water. The suspension is heated to 75 °C while stirring and the pH value is adjusted to 2.0 with 10 % hydrochloric acid. Then 2.67 ml TiCl 4 solution (366 g/1) in 25 ml water are added. During the addition the pH value is maintained at 2.0 by the simultaneous addition of 10 % NaOH solution. Upon completion the suspension is stirred for 15 minutes. Then the suspension is cooled, sucked off, washed and dried over night at 50 °C. Exa ple 6 25 g encapsulated liquid crystal material (Licritherm® TCC-1001) with a solid content of 8.25 g is suspended in 750 ml water. The suspension is heated to 75 °C while stirring and the pH value is adjusted to 1.8 with 5 % NaOH solution. Then 0.96 g . SnCl • 5 H 2 0 in 100 ml water are added. During the addition the pH value is maintained at 1.8 by the simultaneous addi- tion of 10 % NaOH solution. Upon completion the suspension is stirred for 15 minutes. Then the suspension is cooled, sucked off, washed and dried over night at 50 °C. Example 7 25 g encapsulated liquid crystal material (Licritherm® TCC-1001) with a solid content of 8.25 g is suspended in 750 ml water. The suspension is heated to 75 °C while stirring and the pH value is adjusted to 7.0. Then 0.69 g ZnCl 2 in 100 ml water are added. During the addition the pH value is maintained at 7.0 by the simultaneous addition of 10 % NaOH solution. Upon completion the suspension is stirred for 15 minutes. Then the suspension is cooled, sucked off, washed and dried over night at 50 °C. Example 8 25 g encapsulated liquid crystal material (Licritherm® TCC-1001) with a solid content of 8.25 g is suspended in 750 ml water. The suspension is heated to 75 °C while stirring and the pH value is adjusted to 2.0 with 5 % NaOH solution. Then 1.08 g ZrOCl 2 • 8 H0 in 100 ml water are added. During the addition the pH value is maintained at 2.0 by the simultaneous addi- tion of 10 % NaOH solution. Upon completion the suspension is stirred for 15 minutes. Then the suspension is cooled, sucked off, washed and dried over night at 50 °C.

Claims: Claims 1. A thermochromic effect pigment, characterized in that an encapsulated thermochromic liquid crystal is coated with one or more inorganic metal oxides or metal oxide hydrates, mixtures of inorganic metal oxides or metal oxide hydrates or nearly unsoluble metal salts. 2. A pigment according to Claim 1, characterized in that the inorganic metal oxides or metal salts are selected from A1 2 0 3 , Sn0 2 , CaO, Si0 2 , Zr0 2 , Ti0 2 , ZnO, MgO or BaS0. 3. A pigment according to Claims 1 or 2, characterized in that said liquid crystal is coated with a mixed oxide or a mixture of inorganic metal oxide hydrates. 4. A pigment according to Claim 3, characterized in that said mixed oxide or mixture of oxide hydrates contains silicon dioxide. 5. A pigment according to one of the Claims 1 to 4, charac¬ terized in that the liquid crystal is an admixture of at least one chiral component and at least one non-chiral component. 6. A pigment according to Claim 5,- characterized in that at least one chiral component is a compound of the formula I Ri-(Ai-Zi) m -A 2 -R* I wherein R 1 is R* or an alkyl radical or an alkenyl radical with up to 18 C atoms optionally substituted by CN or at least one halogen atom, wherein one or two non-adja¬ cent CH 2 groups of this radicals can also be replaced by -0-, -CO-, -0-CO- and/or -C0-0-, Ai and A 2 are in each case independently of one another a) a 1,4-cyclohexylene group, wherein one or two non-adjacent CH groups can also be replaced by -0- and/or -S- and/or which can be substituted in the 1-position by a CN- or CH 3 -group, b) a 1,4-cyclohexenylene, a piperidine-l,4-diyl or l,4-bicyclo[2,2,2]octylene group, or c) a 1,4-phenylene group optionally substituted by one or two F-atoms or one or two CN- or one or two CH 3 -groups, wherein at least one CH group can also be replaced by N, Zl is -CO-0-, -0-CO-, -CH 2 CH 2 -, -CHCN-CH 2 -, -CH 2 -CHCN-, O H-, -OCH 2 -, -CH 2 O-, -CH=N-, -N=CH-, -NO=N, -N=NO- or a single bond, m is 0, 1, 2 or 3, and R* is a chiral radical imparting optical activity to the compound of the formula I. 7. A pigment according to Claim 5, characterized in that at least one chiral component is a steroid ester of the formula II Ster-0-CO-(Ai-Zi) m -CH 2 -R3 II wherein A 1 , Z 1 and m have the meaning giving for formula I, and R3 is a normal or branched alkyl or alkenyl radical with up to 16 C atoms wherein one CH 2 group may be replaced by -0-, -0-C0- or -C0-0-, and Ster denotes a saturate or unsaturated gonan-3-yl group being optionally substituted by up to 6 normal or branched alkyl radicals with 1 to 10 C atoms. 8. A pigment according to Claim 6, characterized in that R* is a chiral radical of the formula III X Q-C-R Q III wherein Q is a single bond or an alkylene group with 1-8 C atoms, wherein one or two non-adjacent CH 2 groups can be replaced by -CH(CN)-, -CH(F)-, -CH(C1)-, -0-, -S-, -CO-O- or O-CO X is H or CH 3 Y is F, Cl, Br, CN or CH 3 R° is an alkyl residue being different from X with up to 14 C atoms, wherein one or two non-adjacent CH 2 groups may be replaced by -0-, -CO-O- or -O-CO-. A pigment according to at least one of the Claims 5 to 8, characterized in that at least one non-chiral compound is a compound of the formula IV R2- (A3-Z 2 ) p -A"-Z -A5-R4 IV R 2 and R 4 in each case independently of one another are an alkyl radical or an alkenyl radical each with up to 18 C atoms optionally substituted by CN or at least one halogen atom, wherein one or two non-adjacent CH 2 groups of these radicals can also be replaced by -0-, -CO-, -O-CO- and/or -CO-O-, one of R 2 and R 4 may also be CN or halogen. A , A 4 and A 5 are in each case independently of one another a) a 1,4-cyclohexylene group, wherein one or two non-adjacent CH 2 groups can also be replaced by -0- and/or -S- and/or which can be substituted in the 1-position by a CH 3 - or CN-group, b) a 1,4-cyclohexenylene, a piperidine-l,4-diyl or l,4-bicyclo[2,2,2]octylene group, or c) a 1,4-phenyϊene group optionally substituted by one or two F atoms or one or two CH 3 - or one or two CN groups Z2 and Z 3 are each -CO-0-, -O-CO-, -CH 2 CH 2 -, -CHCN-CH 2 -, -CH 2 -CHCN-, -CH=CH-, -OCH 2 -, -CH 2 0-, -CH=N-, -N=CH-, -N=N0-, -N0=N or a single bond, and p is 0, 1 or 2. 10. A coloured lacquer composition, wherein the colourant is a pigment of Claim 1. 11. A coloured paint composition, wherein the colourant is a pigment of Claim 1. 12. A coloured plastic composition, wherein the colourant is a pigment of Claim 1. 13. A dyed fiber composition, wherein the colourant is a pigment of Claim 1. 14. A dyed glass composition, wherein the colourant is a pigment of Claim 1. 15. A dyed cosmetic composition, wherein the colourant is a pigment of Claim 1. 16. A printing ink composition, wherein the colourant is a pigment of Claim 1. 17. A hair colouring agent, wherein the colourant is a pig¬ ment of Claim 1. 18. A process for the production of a thermochromic effect pigment of Claim 1, comprising precipitating one or more inorganic metal oxides or metal oxide hydrates, or nearly unsoluble metal salts in an aqueous medium onto the surface of encapsulated thermochromic liquid crystals suspended in said aqueous medium, and separating and drying the pigment according to known methods. 19. A process according to Claim 18, characterized in that more metal oxides or metal oxide hydrates are precipi¬ tated together or one after another onto the surface of said liquid crystals.

Inventors: HERBSKI MARGARETE, OSTERRIED KARL, SAGE IAN CHARLES, HERBSKI, MARGARETE, OSTERRIED, KARL, SAGE, IAN, CHARLES
Applicants: MERCK PATENT GMBH, MERCK PATENT GESELLSCHAFT MIT BESCHRAENKTER HAFTUNG
Application year: 1992
Main classification: C09K19
IPC codes: A61K8, A61Q1, A61Q5, C03C1, C08K9, C09B67, C09C3, C09D5, C09D7, C09D11, C09K19