SOLVOCHROMIC EFFECT PIGMENTS, METHOD OF PRODUCTION AND USE THEREOF

Abstract

The present invention is directed to effect pigments with solvochromic properties. These effect pigments have a structure comprising a substrate in platelet form and a coating applied to the substrate, wherein the coating comprises: optionally a layer (1) comprising or consisting of at least one of tin oxide, tin hydroxide and/or tin oxide hydrate, a layer (2) comprising at least one of metal oxide, metal hydroxide and/or metal oxide hydrate, and a layer (3) comprising at least one of metal oxide, metal hydroxide and/or metal oxide hydrate, wherein the layers (2) and (3) comprise in their metal oxide, metal hydroxide and/or metal oxide hydrate in a majority two different metal ions from the group consisting of Ti, Fe, Sn or Zr and a further spacer layer (4) being located in between layers (2) and (3), wherein layer (4) has a porous structure comprising cavities and connectors. The solvochromic properties denote to the effect pigment having a first interference color under ambient atmosphere which changes reversibly to a second interference color, when the effect pigment comes into contact with a solvent.

Claims

1. An effect pigment having solvochromic properties comprising substrates in platelet form and a coating applied to the substrates, wherein the coating comprises an optional layer 1 comprising at least one of tin oxide, tin hydroxide and/or tin oxide hydrate, a layer 2 comprising at least one of metal oxide, metal hydroxide and/or metal oxide hydrate, a layer 3 comprising at least one of metal oxide, metal hydroxide and/or metal oxide hydrate, wherein a majority of the metal oxide, metal hydroxide and/or metal oxide hydrate of the layers 2 and 3 comprise two different metal ions selected from Ti, Fe and Zr, and a spacer layer 4 located in between layers 2 and 3, wherein the layer 4 has a porous structure comprising cavities and connectors.

2. The effect pigment having solvochromic properties according to claim 1, wherein the solvochromic properties denote to the effect pigment having a first interference color under ambient atmosphere which changes reversibly to a second interference color, when the effect pigment comes into contact with a solvent.

3. The effect pigment having solvochromic properties according to claim 1, wherein the layer 4 has a median area of cavity size distribution A.sub.50 in a range of 80 to 600 nm.sup.2.

4. The effect pigment having solvochromic properties according to claim 1, wherein the layers 2 and 3 are mainly composed of TiO.sub.2.

5. The effect pigment having solvochromic properties according to claim 1, wherein metal ions comprised in the connectors in the spacer layer 4 are mainly Fe or Zr.

6. The effect pigment having solvochromic properties according to claim 1, wherein the molar ratio of Ti to any of Fe or Zr in layers 2, 3 and 4 is in a range of 1.5 to 4.0.

7. The effect pigment having solvochromic properties according to claim 1, wherein the substrates in platelet form include any one or more of metal platelets, natural mica platelets, synthetic mica platelets, iron mica, glass platelets, SiO.sub.2 platelets, Al.sub.2O.sub.3 platelets, kaolin platelets, talc platelets, and bismuth oxychloride platelets.

8. The effect pigment having solvochromic properties according to claim 1, wherein the average thicknesses of layers 2 or 3 independently are in a range of 40 to 160 nm.

9. The effect pigment having solvochromic properties according to claim 1, wherein the spacer layer 4 has a geometric thickness h.sub.a in a range of 100 to 400 nm.

10. A process for manufacturing an effect pigment having solvochromic properties comprising substrates in platelet form and a coating applied to the substrates, wherein the coating comprises an optional layer 1 comprising at least one of tin oxide, tin hydroxide and/or tin oxide hydrate, a layer 2 comprising at least one of metal oxide, metal hydroxide and/or metal oxide hydrate, a layer 3 comprising at least one of metal oxide, metal hydroxide and/or metal oxide hydrate, wherein a majority of the metal oxide, metal hydroxide and/or metal oxide hydrate of the layers 2 and 3 comprise two different metal ions selected from Ti, Fe and Zr, and a spacer layer 4 located in between layers 2 and 3, wherein the layer 4 has a porous structure comprising cavities and connector, the process comprising: (i) optionally applying an uncalcined layer comprising at least one of tin oxide, tin hydroxide and/or tin oxide hydrate to the substrates in platelet form, (ii) sequentially applying three uncalcined layers A, B and C each consisting essentially of a single metal oxide, metal hydroxide and/or metal oxide hydrate to provide the effect pigment, where the layers A, B and C are arranged directly one on top of another and wherein the metal ions of layers A, B and C are selected from Ti, Fe and Zr, wherein the metal ion from layer B is different to the metal ions of layers A or C, (iii) separating the effect pigment obtained in (ii) from the liquid phase and drying the product, (iv) calcining the dried effect pigment obtained from (iii) at a temperature in a range of 300° C. to 600° C., wherein the metal ions present in layer B diffuse at least partly into layer A and/or layer C during the calcination step to form the layer 4.

11. The process for manufacturing an effect pigment having solvochromic properties as claimed in claim 10, wherein layers A and C are TiO.sub.2 and layer B is Fe.sub.2O.sub.3 or ZrO.sub.2.

12. The process for manufacturing an effect pigment having solvochromic properties as claimed in claim 10, wherein drying the product commences at a temperature ranging from 70° C. to 160° C.

13. The process for manufacturing an effect pigment having solvochromic properties as claimed in claim 10, wherein thicknesses of the layers A and C are independently in a range of more than 50 to 240 nm.

14. The process for manufacturing an effect pigment having solvochromic properties as claimed in claim 10, wherein a stack of the uncalcined layers A, B and C and the optional uncalcined layer comprising at least one of tin oxide, tin hydroxide and/or tin oxide hydrate does not have an additional layer adjacent to the uncalcined layer A or the optional uncalcined layer and/or the uncalcined layer C, the additional layer being composed of any metal oxide including a metal ion selected from Ti, Fe, Sn, Mn, Zr, Ca, Sr, Ba, Ni, Ag, Zn, Cu, Ce, Cr and Co.

15. (canceled)

16. An article comprising a coating which contains an effect pigment having solvochromic properties as claimed in claim 1.

17. The effect pigment having solvochromic properties according to claim 1, wherein the substrates in platelet form comprise metallic substrates coated with at least one of metal oxide, metal hydroxide and/or metal oxide hydrate.

18. The process for manufacturing an effect pigment having solvochromic properties as claimed in claim 10, wherein the substrates in platelet form are nonmetallic.

19. A bronzing composition comprising a binder and the effect pigment having solvochromic properties according to claim 1.

20. A coating application comprising a plurality of layers, a top coating of the plurality of layers comprising the effect pigment having solvochromic properties according to claim 1.

Description

EXAMPLES

Example 1: (Layer Stack: TiO.SUB.2./Fe.SUB.2.O.SUB.3./TiO.SUB.2

[0139] 200 g of synthetic fluorophlogopite with a particle size characteristic (determined with Malvern Mastersizer MS 2000) of D.sub.10=2.3 μm, D.sub.50=7.1 μm, D.sub.90=15.4 μm, Span ΔD=1.85 and an average thickness of about 150 nm were suspended in 1.300 ml water and heated to 85° C. under vigorous stirring. The pH was lowered to 2.2. By adding 50.0 mL of a solution of SnCl.sub.4 (c=55 g/L) within 50 minutes a layer of “SnO.sub.2” was coated on the substrates surface.

[0140] Then the pH-value was further lowered to 1.9 using diluted hydrochloric acid and a solution of 1100 ml TiCl.sub.4 (200 g/l TiO.sub.2) was dosed to the mixture. After 35 h dosing was completed, the mixture was stirred for 10 min and 750 ml of the suspension was removed. Then 620 ml of an aqueous FeCl.sub.3 solution with a density of 1.42 g/cm.sup.3 was added for 6.5 h. Afterwards the mixture was again stirred for 10 min and 1000 ml of the suspension was removed. The pH was lowered to 1.9 and 900 ml of a TiCl.sub.4 (200 g/l TiO.sub.2) solution was dosed within 28.6 h to the mixture. The suspension was filtrated and the filter cake was washed with purified water. The product was dried for 24 h at a temperature of 80° C. in a BINDER WTB vacuum oven under 0.1 bar atmosphere. Finally, the effect pigment was calcined at 500° C. for 45 min in a Nabertherm furnace device equipped with Programm Controller 27.

[0141] Extremely chromatic and highly lustrous effect pigments with solvochromic properties were obtained.

Example 2: (Layer Stack: TiO.SUB.2./Fe.SUB.2.O.SUB.3./TiO.SUB.2

[0142] 100 g of synthetic fluorophlogopite with a particle size characteristic (determined with Malvern Mastersizer MS 2000) of D.sub.10=35.8 μm, D.sub.50=55.2 μm, D.sub.90=112 μm, Span ΔD=1.38 and an average thickness of about 800 were suspended in 1.000 ml water and heated to 90° C. under vigorous stirring. The pH was lowered to 2.2. By adding 25 mL of a solution of SnCl.sub.4 (c=55 g/L) within 50 minutes a layer of “SnO.sub.2” was coated on the substrates surface.

[0143] Then the pH-value was further lowered to 1.9 using diluted hydrochloric acid and a solution of 150 ml TiCl.sub.4 (200 g/l TiO.sub.2) was dosed within 3.33 h to the mixture. After dosing was completed the mixture was stirred for 10 min and the pH was fixed to 2.6. 95 ml of an aqueous FeCl.sub.3 solution with a density of 1.42 g/cm.sup.3 was added within 2 h. Afterwards the mixture was again stirred for 10 min and the pH was lowered to 1.9 and 100 ml of a TiCl.sub.4 (200 g/l TiO.sub.2) solution was dosed within 2.22 h to the mixture. 1000 mL of the suspension were removed before adding further 50 ml of the TiCl.sub.4 solution. The suspension was then filtrated and the filter cake was washed with purified water. The product was dried for 24 h at a temperature of 80° C. in a BINDER WTB vacuum oven under 0.1 bar atmosphere. Finally, the effect pigment was calcined at 500° C. for 45 min using the equipment of Example 1.

[0144] Extremely chromatic effect and highly lustrous pigments with solvochromic properties were obtained.

Example 3: (Layer Stack: TiO.SUB.2./Fe.SUB.2.O.SUB.3./TiO.SUB.2

[0145] 100 g of glass platelets with a particle size characteristic (determined with Malvern Mastersizer MS 2000) of D.sub.10=18.8 μm, D.sub.50=33.1 μm, D.sub.90=57.5 μm, Span ΔD=1.17 and an average thickness of about 1300 nm were suspended in 1,200 ml water and heated to 90° C. under vigorous stirring. The pH was lowered to 2.2. By adding 40 mL of a solution of SnCl.sub.4 (c=25 g/L) within 40 minutes a layer of “SnO.sub.2” was coated on the substrates surface.

[0146] Then the pH-value was further lowered to 1.9 using diluted hydrochloric acid and a solution of 165 ml TiCl.sub.4 (100 g/l TiO.sub.2) was dosed within 5 h to the mixture. After dosing was completed the mixture was stirred for 10 min and the pH was fixed to 2.6. 125 ml of an aqueous FeCl.sub.3 solution with a density of 1.21 g/cm.sup.3 was added within 2.5 h and additionally stirred for one hour. Afterwards the pH was lowered to 1.9 and 85 ml of a TiCl.sub.4 (100 g/l TiO.sub.2) solution was dosed for 5.5 h to the mixture. 1000 mL of the suspension were removed before adding further 10 ml of the TiCl.sub.4 solution. The suspension was then filtrated and the filter cake was washed with purified water. The product was dried for 24 h at a temperature of 80° C. in a BINDER WTB vacuum oven under 0.1 bar atmosphere. Finally, the effect pigment was calcined at 450° C. for 60 min using the equipment of Example 1.

[0147] Extremely chromatic effect pigments with solvochromic properties and significant sparkle were obtained.

Example 4: (Layer Stack: TiO.SUB.2./Fe.SUB.2.O.SUB.3./TiO.SUB.2

[0148] 100 g of synthetic fluorophlogopite with a particle size characteristic (determined with Malvern Mastersizer MS 2000) D.sub.10=10.7 μm, D.sub.50=21.5 μm, D.sub.90=39.2 μm, Span ΔD=1.33 and an average thickness of about 400 nm were suspended in 1.000 ml water and heated to 90° C. under vigorous stirring. The pH was lowered to 2.2. By adding 27.5 mL of a solution of SnCl.sub.4 (c=55 g/L) within 50 minutes a layer of “SnO.sub.2” was coated on the substrates surface.

[0149] Then the pH-value was further lowered to 1.9 using diluted hydrochloric acid and a solution of 300 ml TiCl.sub.4 (200 g/l TiO.sub.2) was dosed within 6.75 h to the mixture. After dosing was completed the mixture was stirred for 10 min and the pH was fixed to 2.6. 220 ml of an aqueous FeCl.sub.3 solution with a density of 1.42 g/cm.sup.3 was added for 4.55 h and additionally stirred for one hour. Afterwards the pH was lowered to 1.9 and 292 ml of a TiCl.sub.4 (200 g/l TiO.sub.2) solution was dosed to the mixture. 1000 mL of the suspension was removed before adding further 25 ml of the TiCl.sub.4 solution. The suspension was then filtrated and the filter cake was washed with purified water. The product was dried for 24 h at a temperature of 80° C. in a BINDER WTB vacuum oven under 0.1 bar atmosphere. Finally, the effect pigment was calcined at 530° C. for 35 min using the equipment of Example 1.

[0150] Extremely chromatic and highly lustrous effect pigments with solvochromic properties were obtained.

Example 5: (Layer Stack: TiO.SUB.2./Fe.SUB.2.O.SUB.3./TiO.SUB.2

[0151] 100 g of synthetic fluorophlogopite with a particle size characteristic (determined with Malvern Mastersizer MS 2000) D.sub.10=10.7 μm, D.sub.50=21.5 μm, D.sub.90=39.2 μm, Span ΔD=1.33 and an average thickness of about 400 nm were suspended in 1.000 ml water and heated to 90° C. under vigorous stirring. The pH was lowered to 2.2. By adding 27.5 mL of a solution of SnCl.sub.4 (c=55 g/L) within 50 minutes a layer of “SnO.sub.2” was coated on the substrates surface.

[0152] Then the pH-value was further lowered to 1.9 using diluted hydrochloric acid and a solution of 560 ml TiCl.sub.4 (200 g/l TiO.sub.2) was dosed within 25 h to the mixture. After dosing was completed the mixture was stirred for 10 min and the pH was fixed to 2.6. 210 ml of an aqueous FeCl.sub.3 solution with a density of 1.42 g/cm.sup.3 was added for 4.5 h and additionally stirred for one hour. Afterwards the pH was lowered to 1.9 and 300 ml of a TiCl.sub.4 (200 g/l TiO.sub.2) solution was dosed to the mixture. 1000 mL of the suspension were removed before adding further 25 ml of the TiCl.sub.4 solution. The suspension was then filtrated and the filter cake was washed with purified water. The product was dried for 24 h at a temperature of 80° C. in a BINDER WTB vacuum oven under 0.1 bar atmosphere. Finally, the effect pigment was calcined at 530° C. for 35 min using the equipment of Example 1.

[0153] Extremely chromatic and highly lustrous effect pigments with solvochromic properties were obtained.

Example 6: (Layer Stack: TiO.SUB.2./ZrO.SUB.2./TiO.SUB.2

[0154] 150 g of synthetic fluorophlogopite with a particle size characteristic (determined with Malvern Mastersizer MS 2000) D.sub.10=10.7 μm, D.sub.50=21.5 μm, D.sub.90=39.2 μm and Span ΔD=1.33 and an average thickness of about 400 nm were suspended in 850 ml water and heated to 75° C. under vigorous stirring. The pH was lowered to 2.2. By adding 40 mL of a solution of SnCl.sub.4 (c=55 g/L) within 75 minutes a layer of “SnO.sub.2” was coated on the substrates surface.

[0155] Then the pH-value was further lowered to 1.9 using diluted hydrochloric acid and a solution of 450 ml TiCl.sub.4 (200 g/l TiO.sub.2) was dosed within 4.7 h to the mixture. After dosing was completed, the mixture was stirred for 10 min, the pH was fixed to 3.8 and 666 ml of a 20 wt.-%, aqueous zirconium tetrachloride solution was dosed for 7.3 h to the mixture. The reaction suspension was stirred for further 3 h. Then the pH-value was further lowered to 1.9 using diluted hydrochloric acid and a solution of 222 ml TiCl.sub.4 (200 g/l TiO.sub.2) was dosed to the mixture. Then 500 mL of the suspension were removed before adding further 25 ml of the TiCl.sub.4 solution. The suspension was then filtrated and the filter cake was washed with purified water. The product was dried for 24 h at a temperature of 80° C. in a BINDER WTB vacuum oven under 0.1 bar atmosphere. Finally, the effect pigment was calcined at 530° C. for 35 min using the equipment of Example 1.

[0156] Extremely chromatic and highly lustrous effect pigments with solvochromic properties were obtained.

Example 7: (Layer Stack: TiO.SUB.2./Fe.SUB.2.O.SUB.3./TiO.SUB.2

[0157] 215 g of an aluminum flake paste (STAPA METALLUX 214, s.c.: 69%, Eckart GmbH) were suspended in 650 g ethanol for 10 min. Thereafter 20 g water (in fully desalted quality) were added and the mixture was heated to 75° C. The pH was adjust with acetic acid to 5.0 and a 1:1 vol/vol mixture of 330 ml of Titan(IV)isopropylate und isopropyl alcohol were dosed for 11 h. Afterwards 10 g water were added and the mixture was stirred for 30 min. Afterwards 200 ml of an ethanolic FeCl.sub.3 solution (w(FeCl.sub.3)=40.0 wt.-% were dosed at constant pH 5.5 which was adjusted by addition of an ethanolic NaOH solution (10 wt.-% NaOH) within 6.7 h. Afterwards the mixture was stirred for 30 min and then 340 ml of a 1:1 vol/vol mixture of Titan(IV)isopropylate und isopropyl alcohol were constantly dosed at an rate of 0.5 mL/min at pH 5.0. Afterwards the suspension was stirred for further 60 min and then the hot mixture was filtrated with a Buchner funnel and was washed with a 1.1 vol/vol mixture of water and ethanol. Finally, the filter cake was washed with ethanol to remove water and was dried under N.sub.2-atmosphere at 100° C. for 17 hours. The dried metal effect pigment powder was further treated under nitrogen at 450° C. for 60 min using the equipment of Example 1.

[0158] Metal effect pigments with an orange-colored absorption color and a solvochromic effect were obtained.

[0159] If not mentioned otherwise, feed rates for same chemicals in the recipes were kept constant.

[0160] Comparative Example 1: Example 1 of EP 3234024 A1.

[0161] Comparative Example 2: Example 5 of EP 3034563 A1.

[0162] Comparative Example 3: Example 3 of EP 3234024.

[0163] Comparative Example 4: Example 10 of EP 3234024 A1

[0164] Comparative Example 5: Example 6 of EP 3 234 024 A1.

[0165] Comparative Example 6: Example 4 of EP 3 234 025 A1.

[0166] Comparative Example 7: Example 1 of EP 3 234 025 A1.

[0167] Comparative Example 8: Example 3 of EP 3 234 025 A1.

[0168] Comparative Example 9: “Xirona Le Rouge”

[0169] Pearlescent pigment from Merck consisting of Fe.sub.2O.sub.3 coated SiO.sub.2 flakes.

[0170] Comparative Example 10: “Magic Mauve”.

[0171] Color shifting pearlescent pigment from Merck consisting of TiO.sub.2 coated SiO.sub.2 flakes.

[0172] Comparative Example 11: Iriodin 307:

[0173] Multilayer pearlescent pigment from Merck with layer stack: TiO.sub.2/Fe.sub.2O.sub.3/SiO.sub.2/TiO.sub.2.

[0174] II Characterization of the Solvochromic Effect Pigments and Pigments from Comparative Examples

[0175] IIa Particle Size Measurement

[0176] The size distribution curve of the absorbent effect pigments of the invention and of the pigments from the comparative examples was determined using the Malvern Mastersizer 2000 instrument, according to the manufacturer's instructions and using an appropriate SOP. For this purpose, about 0.1 g of the respective pigment was introduced into the sample preparation cell of the measuring instrument by means of a Pasteur pipette as an aqueous solution, without addition of dispersing aids, with constant stirring, and analyzed repeatedly. The individual measurement results were used to form the medians. The scattered light signals were evaluated by the Fraunhofer method as volume-weighted values of equivalent spheres.

[0177] The median particle size D.sub.50 in the context of this invention is understood to mean the D.sub.50 of the cumulative frequency distribution of the volume-averaged size distribution function. The D.sub.50 indicates that 50% of the pigments have a diameter equal to or less than the value reported, for example 20 μm. Correspondingly, the D.sub.10 and D.sub.90 respectively state that 10% and 90% of the pigments have a diameter equal to or less than the respective measured value. The span ΔD, defined as

[00003]$\Delta D=\frac{D_{90}-D_{10}}{D_{50}}$

is a common indication value characterizing the breadth of the particle size distribution. With regard to the visual appearance of the absorbent effect pigments of the invention, a small value of ΔD, i.e. a narrow span, is preferred.

TABLE-US-00002 TABLE 2 Particle size distribution data of Examples and Comparative Examples Example/ D.sub.10 D.sub.50 D.sub.90 Comparative Example [μm] [μm] [μm] Span Example 1 4.1 9.5 17.7 1.44 Example 2 22.0 52.7 108.3 1.64 Example 3 16.4 32.6 58.9 1.30 Example 4 7.8 18.3 30.1 1.55 Example 5 11.7 23.0 41.6 1.30 Example 6 12.3 23.6 42.4 1.27 Example 7 12.4 23.2 41.9 1.27 Example 8 9.3 22.0 40.6 1.43 Example 9 20.6 35.9 58.2 1.05 Comparative 10.8 22.5 40.6 1.33 Example 1 Comparative 10.5 23.6 42.8 1.37 Example 2 Comparative 12.4 23.7 42.1 1.25 Example 3 Comparative 8.8 20.1 37.6 1.43 Example 4 Comparative 9.3 20.9 39.7 1.48 Example 5 Comparative 9.2 20.7 39.7 1.48 Example 6 Comparative 10.0 21.9 40.2 1.38 Example 7 Comparative 8.3 20.7 40.8 1.567 Example 8 Comparative 9.7 19.3 35.5 1.34 Example 9 Comparative 8.8 20.7 39.8 1.50 Example 10 Comparative 11.5 23.4 43.9 1.38 Example 11

[0178] IIb Angle-Dependent Color Measurements; Characterization of Solvochromic Effect

[0179] To measure the color and brightness values, the effect pigments of the invention and some of the pigments from the comparative examples were stirred into a conventional nitrocellulose lacquer (Erco 2615e bronze mixing lacquer colorless; from Maeder Plastiklack AG at a pigmentation level of 6% by weight, based on the total weight of the wet lacquer. This was done by initially charging the respective pigments and then dispersing them into the lacquer with a brush. The finished lacquer was applied to black/white hiding charts (Byko-Chart 2853, from Byk Gardner) in a wet film thickness of 40 μm or of 76 μm (example 4) with a spiral applicator on an applicator drawdown apparatus (RK Print Coat Instr. Ltd. Citenco K 101 drawdown apparatus), and subsequently dried at room temperature. The choice of spiral applicator depends on the size of the effect pigments: for pigments with D.sub.50-values of smaller then 40 μm a spiral applicator of 40 m and for pigments with D.sub.50-values of 40 to 85 μm a 76 μm spiral applicator was used.

[0180] The such prepared drawdowns have been wetted with a tiny amount of an isopropanol/water 1:1 (w/w) mixture for 20 seconds and afterwards the supernatant was removed by wiping with a lint-free cloth. A visual color change could be observed in case of the inventive examples. After several minutes, when the surface started to dry, the color changed back repeatedly to the original color. This procedure was repeated at least 10 times. Here, the color impression was reported qualitatively as on wetted parts of the draw-downs color measurements are not feasible. The results for all samples are depicted in table 3.

[0181] All inventive examples show a solvochromic effect which was reversible for at least ten cycles. All comparative examples did not exhibit a visible color change upon wetting and therefore exhibited no solvochromic effect.

[0182] In order to more quantify the solvochromic effect another series of experiments were conducted. The draw-downs described above were partially coated with a clear lacquer. Therefore, a commercially available acrylate based clear lacquer was used which was applied with a thickness of 40 μm of the wet coating on the hiding charts. With this clear lacquer additional organic solvent is introduced which could come into contact with the effect pigments embedded in the coating beneath.

[0183] A BYK-mac multi-angle colorimeter (from Byk-Gardner) was used to determine the color values on the black background of the hiding chart at a constant angle of incidence of 45° (according to the manufacturer's instructions) at various observation angles relative to the specular angle. Characterization of the color tone was accomplished using especially the Hue value's H*.sub.15°, which were measured at a measurement angle separated by 15° from the specular angle on the black background of the black/white hiding chart. Measurements at this angle essentially characterize the interference color of the effect pigments.

[0184] After drying the area coated with the clear lacquer was measured on black background sites using the BYK-mac instrument. To characterize the solvochromic effect the difference of the Hue ΔH*.sub.15 according to the formula (II) was used:

ΔH*=H*.sub.15°(CC)−H*.sub.15° (woCC)  (II)

[0185] Herein H*.sub.(15° CC) is the Hue at 15° measured on the clear lacquer and H*.sub.(15° woCC) is the Hue at 15° measured on the application without clear lacquer coating.

[0186] The difference ΔH*.sub.15° is a measure of the color shift which can be reached if the coating is pigmented with the solvochromic effect pigments and is treated with additional solvents and therefore kind of represents a “frozen” solvochromic effect.

[0187] The absolute values of the color changes are of course dependent on the refractive index of the dried clear lacquer film. The results of the measurements are depicted in table 3.

TABLE-US-00003 TABLE 3 Results of visual color determination of wetting experiments and measured Hue's at 15º of Examples and various Comparative Examples with and without clear coating Color of Color Drawdown Color of drawdown change Sample before wetting after wetting for 10x? H*.sub.(15°CC) H*.sub.(15ºwoCC) ΔH*.sub.(15º) Example 1 Orange Olive green yes 109.04 71.3 37.77 Example 2 Orange sparkeling Light green yes 91.56 78.2 13.35 Example 3 Yellow Green yes 85.96 62.7 23.23 Example 4 Light bluish green Intense yellowish green yes 151.61 114.5 37.10 Example 5 Brick red Orange yes 64.89 45.3 19.63 Example 6 Orange Pinkish red yes 56.12 78.9 −22.83 Example 7 Brick red metallic Orange metallic yes 45.7 36.2 9.47 Comparative Example 1 Gold Gold no 99.7 95.62 −4.08 Comparative Example 2 Gold dark Gold dark no Comparative Example 3 Blue Blue no Comparative Example 4 Intense Red Intense Red no 33.3 30.04 −3.26 Comparative Example 5 Intense Red Intense Red no 7.2 9.64 −2.48 Comparative Example 6 Red Red no 36.0 40.8 4.81 Comparative Example 7 Intense red Intense red no 7.5 11.0 −3.5 Comparative Example 8 Intense red Intense red no Comparative Example 9 Intense red Intense red no 23.86 26.31 2.45 Comparative Example 10 Violet Violet no 91.87 91.30 −0.57 Comparative Example 11 Gold Gold no 354.8 352.2 −2.6

[0188] By coating with the clear lacquer the effect pigments located in the base coat beneath come into contact with solvent from the clear coating. All inventive Examples exhibit a rather strong shift of ΔH*.sub.(15°) which is an indication of a strong solvochromic effect. The pigments of the Comparative Examples in contrast exhibit a much smaller shift of ΔH*.sub.(15°), even if they are so called “color-flopper” such as comparative example 10. This color-flopper pigment exhibits a strong angle dependence of the color, but does not show a significant solvochromic effect.

[0189] The solvochromic effect is dependent on the gaseous pressure of the solvent and is reversible. By coating with a clear coating this effect can be frozen and better made quantifiable as described above.

[0190] Like all the effect pigments of the inventive examples the comparative examples 1 to 8 do have a porous spacer layer. However, only the inventive examples exhibit the solvochromic effect.

[0191] IIc X-Ray Fluorescence Analysis (XRF)

[0192] The metal oxide, metal hydroxide and/or metal oxide hydrate contents of the solvochromic effect pigments of the invention and of the pigments from the comparative examples were determined by means of x-ray fluorescence analysis (XRF). For this purpose, the respective pigments were incorporated into a lithium tetraborate glass tablet, fixed in solid sample measuring cups and analyzed therefrom. The measuring instrument used was the Advantix ARL system from Thermo Scientific. The results are shown in table 4. The figures for the different contents are reported here as TiO.sub.2 for titanium, as Fe.sub.2O.sub.3 for iron, as SnO.sub.2 for tin and as ZrO.sub.2 for zirconium. Furthermore, the molar ratio of the content of Ti to Fe or to Zr in their elemental form is depicted.

TABLE-US-00004 TABLE 4 Physical Characterization of Examples and Comp. Examples: Ratio Ti/Fe SEM- analysis or Ti/Zr Initial layer stack h.sub.l2 h.sub.l3 h.sub.a A.sub.50/ XRF (wt .- % as oxide) (elemental, Sample before calcination [nm] [nm] [nm] [nm.sup.2] Ti Fe Sn Zr molar Example 1 TiO.sub.2/Fe.sub.2O.sub.3/TiO.sub.2 80 92 110 113 52.5 22.7 0.25 2.0 Example 2 TiO.sub.2/Fe.sub.2O.sub.3/TiO.sub.2 68 74 116 182 30.6 13.2 0.47 2.0 Example 3 TiO.sub.2/Fe.sub.2O.sub.3/TiO.sub.2 49 98 124 203 24.5 10.8 0.39 1.9 Example 4 TiO.sub.2/Fe.sub.2O.sub.3/TiO.sub.2 54 113 130 164 42.5 19.8 0.36 1.8 Example 5 TiO.sub.2/Fe.sub.2O.sub.3/TiO.sub.2 153 79 128 241 51.9 17.5 0.32 2.5 Example 6 TiO.sub.2/ZrO.sub.2/TiO.sub.2 79 39 163 368 46   / 0.15 23.2 1.6 Example 7 TiO.sub.2/Fe.sub.2O.sub.3/TiO.sub.2 43 51 86 156 22.5 34.2 / / 1.7 Comparative Example 1 TiO.sub.2/Fe.sub.2O.sub.3/TiO.sub.2/ 85 91 20 4,944 57.7 6.9 0.78 / 7.2 Fe.sub.2O.sub.3 Comparative Example 2 Fe.sub.2O.sub.3/TiO.sub.2/Fe.sub.2O.sub.3/TiO.sub.2/ 85 91 24 1,362 37.8 7.3 / / 4.4 Fe.sub.2O.sub.3 Comparative Example 3 TiO.sub.2/Fe.sub.2O.sub.3/TiO.sub.2/ 66 65 20 1,288 47.2 5.8 0.55 / 7.0 Fe.sub.2O.sub.3 Comparative Example 4 Fe.sub.2O.sub.3/TiO.sub.2/Fe.sub.2O.sub.3 118 82 18 382  9.1 51.1 / / 0.2 Comparative Example 5 Fe.sub.2O.sub.3/SnO.sub.2/Fe.sub.2O.sub.3 70 99 35 65,511 / 65.8 4.3  0.0 Comparative Example 6 (SnO.sub.2)/TiO.sub.2/SnO.sub.2/ 113 113 56 5,296 25.8 34.4 3.4  0.6 Fe.sub.2O.sub.3 Comparative Example 7 Fe.sub.2O.sub.3/SnO.sub.2/Fe.sub.2O.sub.3 67 107 46 20,402 / 55.9 3.8  0.0 Comparative Example 8 Fe.sub.2O.sub.3/SnO.sub.2/Fe.sub.2O.sub.3 8,512 0.0 Comparative Example 9 Fe.sub.2O.sub.3 / / / / / 57.7 / Comparative Example 10 SnO.sub.2/TiO.sub.2 / / / / 10.4 / 2.3  Comparative Example 11 TiO.sub.2/Fe.sub.2O.sub.3/SiO.sub.2/TiO.sub.2 / / / / 27.1 18.8 0.4  h.sub.l2 [nm] = average thickness of layer 2; h.sub.Sl3 [nm] = average thickness of layer 3 h.sub.a [nm] = average thickness of porous layer 4 A.sub.50 [nm.sup.2]: median of area size distribution of cavities in porous layer 4

[0193] IId Determination of the Mean Thickness of the Substrates in Platelet Form, the Mean Layer Thickness of Layers 2 and 3, the Mean Layer Thickness of the Overall Coating, the Mean Height h.sub.a of the Spacer Layer and the Area Size Distribution a of the Cavities with SEM

[0194] For this purpose, the effect pigments of the examples and comparative examples were incorporated in a concentration of 10 wt.-% into a two-component clearcoat, Autoclear Plus HS from Sikkens GmbH, with a sleeved brush, applied to a film with the aid of a spiral applicator (wet film thickness 26 μm) and dried. After a drying time of 24 h, transverse sections of these applicator drawdowns were produced. The transverse sections were analyzed by SEM (Zeiss supra 35) (using the SE (secondary electrons) detector). To determine the mean layer thickness of layers 2 and 3, the mean thickness of the overall coating, the mean height h.sub.a of the spacer layer and the median of the area size distribution A.sub.50 of the cavities, the upper and lower substrate surfaces, i.e. the longer side of the substrate in platelet form recognizable in each case in the SEM transverse section, were each used as the baseline. The baseline was drawn here along the surface of the substrate in platelet form in the scanning electron micrograph of the transverse section by connecting the two points of intersection of nonmetallic substrate in platelet form—optional layer 1 or of nonmetallic substrate in platelet for—layer 2 from the left—and right-hand edges of the scanning electron micrograph of the transverse section to one another by means of a straight line. The scanning electron micrographs of transverse images were analyzed with the aid of the AxioVision 4.6.3 image processing software (from Zeiss).

[0195] A sufficient number of parallel lines were drawn at 50 nm intervals at a 90° angle from these two baselines as to place a grid over the complete scanning electron micrograph of the transverse section of the effect pigment as depicted exemplary in FIG. 1 which represents an effect pigment with layers 2 and 3 and a spacer layer from state-of-the-art effect pigments. In this figure an effect pigment having a so-called “spacer layer” from the state of the art is shown. The magnification of the scanning electron micrograph of the transverse section was preferably at least 50,000-fold, based on Polaroid 545. Proceeding from the respective upper and lower baselines of the nonmetallic substrate in platelet form in the direction of layer 3 in each case, the distances between the points of intersection of these lines at the respective interfaces of the optional layer 1 with layer 2, of layer 2 with the spacer layer 4, of spacer layer with layer 3 and of layer 3 with the environment were measured manually.

[0196] These measurements yielded the layer thicknesses of layer 2 (h.sub.l2) and of layer 3 (h.sub.l3), the thickness of the overall coating (h.sub.tot), and the height h.sub.a of the spacer layer by formation of differences. Height h.sub.a is the overall coating thickness (h.sub.tot) minus thickness of layer 2 (h.sub.l2) minus thickness of layer 3 (h.sub.l3).

[0197] The individual values of the layer thicknesses, the height h.sub.a that have been determined in this way were used to form the respective arithmetic means in order to determine the above-specified values for the mean layer thicknesses and the mean height h.sub.a. To be statistically meaningful, the above-described measurements were conducted on at least 60 lines. The term “mean” in all cases means the arithmetic mean.

[0198] Cross sections of the pigments of the comparative examples which exhibit a spacer layer were characterized in the same manner as described above.

[0199] Examples of SEM-cross section micrographs at a magnification of 50,000-fold (against Polaroid 545) are depicted in FIG. 2 (example 2) and FIG. 3 (example 6). The three-layer structure (layers 2, 3, and in between spacer layer 4) can be well resolved. The spacer layer for example 2, as seen in this two-dimensional picture, has sort of a “teeth”-like morphology whilst the spacer layer of example 6 has sort of a “sponge”—like morphology. These morphologies are representative for the solvochromic effect pigments with various states in between.

[0200] In contrast, SEM pictures of comparative example 1 (FIG. 4) and of comparative example 4 (FIG. 5) are shown. In comparative example 1 the spacer layer is very clearly seen and it is striking that it has much more cavities and larger cavities than in the inventive examples. Comparative example 4, in contrast, has a very thin spacer layer only.

[0201] To more quantify these morphology differences the area distribution functions of the cavities in the spacer layers were determined for the inventive examples and those comparative examples which exhibit a spacer layer. For this purpose the micrographs were processed again with the microscope software AxioVision for all inventive examples and for comparative examples 1 to 8. At least 32 cavities were measured individually. For the inventive examples at least 120 cavities were measured. The cavities were first segmented using the software, their areas were measured and afterwards the cumulative frequency distribution was evaluated. With the quantile function of excel the A.sub.50-values were determined and reported in Table 4.

[0202] Additionally, the determined size distributions of the A-values were depicted in FIG. 6.

[0203] Clearly the A.sub.50-values as well as the whole cavity area A distribution were much lower for all inventive examples compared to the values of the comparative examples. Only for comparative example 4 the A.sub.50-value was close to those of inventive examples, but here the layer stack was different (Fe.sub.2O.sub.3/TiO.sub.2/Fe.sub.2O.sub.3).

[0204] All inventive examples exhibit a layer stack of either TiO.sub.2/Fe.sub.2O.sub.3/TiO.sub.2 or of TiO.sub.2/ZrO.sub.2/TiO.sub.2 before calcination.

[0205] It is assumed that the rather small cavity sizes lead to a high inner surface area of the connectors which is capable to evolve high capillary forces. With the help of these capillary forces the cavities may be filled with solvent. This change in the effective refractive index of this layer causes a difference in the interference color. If the solvent can evaporate it is assumed that the capillary forces are not strong enough to keep the solvent molecules in the spacer layer so that they can disappear.

[0206] Additionally, it can be seen from Table 4 that all inventive examples have a strikingly different Ti/Fe- or Ti/Zr-ratio compared to the comparative examples.

LIST OF FIGURES

[0207] FIG. 1: SEM of a cross-section of a “spacer” effect pigment from state-of-the art. Magnification: 50,000 against Polaroid 545.

[0208] FIG. 2: SEM of a cross-section of the effect pigment of example 2. Magnification: 50,000 against Polaroid 545.

[0209] FIG. 3: SEM of a cross-section of the effect pigment of example 6. Magnification: 50,000 against Polaroid 545.

[0210] FIG. 4: SEM of a cross-section of the effect pigment of comparative example 1. Magnification: 50,000 against Polaroid 545.

[0211] FIG. 5: SEM of a cross-section of the effect pigment of example 4. Magnification: 50,000 against Polaroid 545.

[0212] FIG. 6: Cumulative frequency distributions of the pore area distribution as determined from SEM micrographs for several examples and comparative examples.