EFFECT PIGMENTS HAVING A REFLECTIVE CORE

Abstract

The present invention relates to an effect pigment having optically active layers consisting of a flake of a highly reflective material with directly adjacent on one side or on both sides a layer of a semiconducting material having a bandgap of 0.1 to 3.5 eV. The effect pigment may be further coated with a coating which is optically non-active in the visible wavelength region.

Claims

1. An effect pigment comprising optically active layers, the optically active layers consisting of a flake of a highly reflective material and a layer of a semiconducting material directly adjacent on one side or on both sides of the flake, the semiconducting material having a bandgap of 0.1 to 3.5 eV.

2. The effect pigment according to claim 1, wherein the effect pigment is further encapsulated with an outer optically non-active layer.

3. The effect pigment according to claim 1, wherein the highly reflective material comprises aluminum, copper, chromium, titanium or gold.

4. The effect pigment according to claim 1, wherein the semiconductor material having a bandgap of 0.1 to 3.5 eV comprises germanium, silicon, an alloy of germanium and silicon, silicon monoxide, a non-stoichiometric chromium oxide (CrO.sub.x) or a non- stoichiometric aluminum oxide (AlO.sub.x).

5. The effect pigment according to claim 4, wherein the semiconductor material having a bandgap of 0.1 to 3.5 eV comprises germanium, silicon, or an alloy of germanium and silicon.

6. The effect pigment according to claim 1, wherein the flake of a highly reflective material has an average thickness in the range from 5 to 500 nm.

7. The effect pigment according to claim 1, wherein the at least one layer of the semiconductor material has a mean thickness in the range from 5 to 200 nm.

8. The effect pigment according to claim 1, the effect pigment including an optically non-active layer, wherein the optically non-active layer comprises one or more of a layer including Mo-oxide, a layer including SiO.sub.2, a layer including Al.sub.2O.sub.3, and a layer including a surface modifier.

9. The effect pigment according to claim 1, wherein the flake of a highly reflective material comprises aluminum and the semiconductor material having a bandgap of 0.1 to 3.5 eV comprises germanium, silicon, or an alloy of germanium and silicon.

10. A method of manufacturing an effect pigment comprising optically active layers, the optically active layers consisting of a flake of a highly reflective material and a layer of a semiconducting material directly adjacent on both sides of the flake, the semiconducting material having a bandgap of 0.1 to 3.5 eV, the method using a PVD process comprising: coating a thin, flexible substrate with a release coat agent, depositing semiconductor layer 1 onto the flexible substrate using a roll-to-roll process, depositing a layer of a reflective metal onto the semiconductor layer 1, depositing a second semiconductor layer 2 onto the reflective metal layer, and stripping a material stack comprising the semiconductor layer 1, the reflective metal, and the second semiconductor layer from the flexible substrate in a solvent.

11. The method of manufacturing according to claim 10, wherein the reflective metal has a thickness in a range of 5 to 500 nm.

12. The method of manufacturing according to claim 10, wherein the semiconductor layer 1 and semiconductor layer 2 are composed of the same material.

13. The method of manufacturing according to claim 10, wherein the semiconductor layers 1 and 2 have the same thickness.

14. A coating composition comprising an effect pigment according to claim 1 and a binder.

15. The coating composition according to claim 14 having a flop index in the range of 30 to 200.

16. The effect pigment according to claim 1, the effect pigment including an optically non-active layer, wherein the optically non-active layer comprises one or more of a layer including Mo-oxide, a layer including SiO.sub.2, a layer including Al.sub.2O.sub.3, a layer including an organofunctional silane, a layer including a phosphate ester, a layer including a phosphonate ester, and a layer including a phosphite ester.

17. An ink composition comprising an effect pigment according to claim 1 and a binder.

18. The ink composition according to claim 17 having a flop index in the range of 30 to 200.

19. The method of claim 10, further including particle sizing, particle classification and solvent dispersion steps.

Description

EXAMPLES

Pre-Examples 1: 2-layer Material (Al—Ge)

[0059] A layer of 1.0 – 1.5 optical density (OD) aluminium was deposited on a 30 cm wide clear polyester film coated with a CAB (cellulose acetobutyrat) based release agent using ebeam PVD evaporation. Enough Al was deposited onto the web to complete the second step below and provide an Al-only web for comparison. The ebeam source was positioned 36 cm below the web during process and webspeed was held at a constant 9 m/min. The ebeam source accelerating voltage was held at a constant 10 kV throughout the run. In the second step, a layer of Ge was deposited on top of the aluminium layer. Ebeam current was varied per condition. The web was stopped and the shutter closed during condition changes, which provided a clear visible condition delineation during post-run web observations.

[0060] Using the set-up described above, Ge with different thickness were deposited on the aluminium layer, giving a colouration from blue (thicker layers) to red (thinner layers). The results are summarised in Table 1.

TABLE-US-00001 Example Ge-depostion Ebeam current (A) Colour 1a 0 Silver 1b 0.180 Light yellow 1c 0.190 Gold 1d 0.200 Orange 1e 0.220 Magenta 1f 0.240 Blue 1g 0.250 Teal 1h 0.260 Teal-silver

Examples 2: 3-layer Material (Ge—Al—Ge)

[0061] In a similar set-up as in example 1, 3-layer materials were produced. The ebeam source was positioned 36 cm below the web during process and webspeed was held at a constant 10 m/min. The ebeam source accelerating voltage was held at a constant 10 kV throughout the run. In a first step a Ge-layer was deposited on a clear polyester film with a release coat layer using PVD ebeam evaporation. Rudimentary in-situ optical transmission sensors were utilized to determine the germanium thickness, and ebeam current was manipulated to target appropriate germanium thickness. In a next step an Al layer was deposited corresponding to approximately 0.9 - 1.5 OD. Optical transmission sensors in combination with current adjustment was utilized to target appropriate Al thickness. A third process step a further layer of Ge was deposited. Again, in-situ optical transmission sensors were utilized to determine the germanium thickness, and ebeam current was manipulated to target appropriate germanium thickness. The thickness of the 2 germanium layers was targeted to be the same, so that the webside and metal side of each condition would be the same colour. Orange, purple, and blue colouration were targeted and successfully produced in 3 separate conditions. The colouration of the web and metal side of the films matched well in each material set.

[0062] The process conditions are summarized in Table 2

TABLE-US-00002 Example In-situ Optical Trans (%) Average Ge layer thickness (nm) In-situ Optical Trans (%) Average Al Layer thickness (nm) 2a 63 10 19 25 nm 2b 49 14.5 18 25 nm 2c 40 29 19 20 nm

[0063] The materials obtained in Example 2 were all stripped from the polyester film and milled/crushed to a particles size listed below (D50 value). Pigments were prepared with a 20 wt.% in GEPM. Inks were prepared using a total metals content specified below in Eckart’s in-house LQ5797 nitrocellulose binder system. The samples were drawn down on a flat BYK drawdown card. Gloss data were collected using a BYK Micro Tri-gloss meter. Additional optical data were collected using a BYK Mac meter. The results of these measurements are summarised in Table 3.

TABLE-US-00003 Optical data of Examples 2 Sample Particle Size D50 (.Math.m) Metals Content (%) Gloss 60° Gloss 85° Flop Index L*.sub.(15°) (trans) L*.sub.15° L*.sub.45° a*.sub.15° b*.sub.15° Visual colour 2a 15 2.5 97.6 61.6 28.1 127.8 106.3 24.3 7.5 26.2 Orange 2b 11 4.5 52.8 78.5 43.4 95.4 78.1 10.6 14.4 -3.1 Purple 2c 11 4.5 55.0 75.4 43.7 93.3 75.9 10.1 -9.7 -17.9 Blue

Examples 3: 3-Layer Material (Ge—Al—Ge) and Effect Pigments

[0064] In a similar set-up as in example 2, 3-layer materials were produced. The ebeam source was positioned 36 cm below the web during process and webspeed was held at a constant 10 m/min. The ebeam source accelerating voltage was held at a constant 10 kV throughout the run. In a first step a Ge-layer was deposited on a clear polyester film with a release coat layer using PVD ebeam evaporation. Ebeam current was set at the beginning of the run and webspeed was utilized to manipulate the germanium layer thicknesses. In a next step an Al layer was deposited corresponding to approximately 1.0 - 1.5 OD. Optical transmission sensors in combination with current adjustment was utilized to target appropriate Al thickness. In a third process step a further layer of Ge was deposited using the same parameters as the first step. Again, ebeam current was set at the beginning of the run, but in this example webspeed was utilized to manipulate the germanium layer thicknesses. The thickness of the 2 germanium layers was targeted to be the same, so that the webside and metal side of each condition would be the same colour. Yellow, orange, burgundy, royal blue, and teal colouration were successfully produced. The colouration of the web and metal side of the films matched well in each material set.

[0065] The materials obtained in Example 3 were all stripped from the polyester film and milled/crushed to a particle size of approximately 20 microns (D50 value). Pigments were prepared with a 20 wt.% in GEPM. Inks were prepared using a total metals content specified below in Eckart’s in-house LQ5797 nitrocellulose binder system. The samples were drawn down on a flat BYK drawdown card. Gloss data were collected using a BYK Micro Tri-gloss meter. A comparison to commercially available Metalure Liquid Black is shown in Table 4, comparative example 3f. Additional optical data were collected using a BYK Mac meter. The results of these measurements are summarised in Table 4. Further the normalized spectral response at 15 degrees of materials 3a - 3f is shown in FIG. 1.

TABLE-US-00004 Optical values for Examples 3 Sample Metals Content (%) Gloss 60° Flop Index L.sub.(-15°) (trans) L.sub.15° L.sub.45° a*.sub.15° b*.sub.15° Visual colour 3a 3.0 147 41.1 114.0 93.4 14.0 7.6 24.6 Gold 3b 3.5 114 43.0 101.6 82.0 11.3 9.6 20.9 Orange 3c 4.0 82.9 52.5 86.4 69.3 7.3 12.1 10.3 Burgundy 3d 4.5 66.6 75.7 63.9 49.1 3.1 5.5 -17.3 Royal Blue 3e 5.0 65.8 46.7 91.2 74.9 9.1 -7.7 -10.5 Teal 3f.sup.# 3.2 62.0 31.0 110.4 92.2 19.0 -2.0 -3.5 Dark Chrome .sup.#): Comparative example

Examples 4: 3 Layer Material (Ge—Cu—Ge)

[0066] In a similar set-up as in example 1, a 3-layer material was produced with Cu as the central metallic layer. The ebeam source was positioned 36 cm below the web during process and webspeed was held at a constant 10 m/min. The ebeam source accelerating voltage was held at a constant 10 kV throughout the run. In a first step a Ge-layer was deposited on a clear polyester film with a release coat layer using PVD ebeam evaporation. Rudimentary in-situ optical transmission sensors were utilized to determine the germanium thickness, and ebeam current was manipulated to target appropriate germanium thickness. In order to target a red colouration, a Ge thickness target of approximately 10 nm was targeted by utilizing SEM and optical data obtained from example 2. In a next step a Cu layer was deposited corresponding to approximately 2.0 - 3.0 OD. Optical transmission sensors in combination with current adjustment was utilized to target appropriate Cu thickness. According to SEM micrographs, a Cu thickness of approximately 50 nm was achieved. A third process step a further layer of Ge was deposited. Again, in-situ optical transmission sensors were utilized to determine the germanium thickness, and ebeam current was manipulated to target appropriate germanium thickness. The thickness of the 2 germanium layers was targeted to be the same, so that the webside and metal side of each condition would be the same colour. Red colouration was targeted and successfully produced in 3 separate conditions. The colouration of the web and metal side of the films matched well in each material set.

[0067] The materials obtained in Example 4 were all stripped from the polyester film and milled/crushed to a particles size of approximately 15 microns (D50 value). Pigments were prepared with a 23 wt.% in GEPM. Cu-based PVD pigments are typically difficult to stabilize, however, the germanium surface coating appears to impart at least some chemical stability, allowing the pigments to be post-processed without substantial optical degradation. Inks were prepared using a total metals content of 6.0% in Eckart’s in-house LQ5797 nitrocellulose binder system. The samples were drawn down on a flat BYK drawdown card. Optical data for a sample of Metalure Liquid Black (4b) at 3.2% solids is shown for comparison. Gloss data were collected using a BYK Micro Tri-gloss meter. Additional optical data were collected using a BYK Mac meter. The results of these measurements are summarised in Table 5a and 5b.

TABLE-US-00005 Sample Metal Content (%) Gloss 20° Gloss 60° Flop Index L*.sub.(-15°) (trans) L*.sub.15° L*.sub.45° Visual colour Ex. 4a 6.0 21.9 63.0 25.5 129.6 109.5 27.4 Red Comp-Ex. 4b 3.2 20.0 62.0 31.0 110.4 92.2 19.0 Dark Chrome

TABLE-US-00006 a*,b* values for Examples 5 Sample a*15 a*25 a*45° a*75° a*110° b*15° b*25° b*45° b*75° b*110 Ex. 4a 20.7 14.4 8.5 6.5 6.5 20.9 14.9 8.7 6.2 5.8 Comp. Ex. 4b -1.9 -0.8 -0.3 -0.1 -0.1 -3.5 -0.6 0.5 0.4 0.27

Pre-Example 5: 2 Layer Film (Cr—CrOx)

[0068] In a similar set-up as in example 1, 2-layer films were produced with Cr as the first metallic layer. The ebeam source was positioned 36 cm below the web during process. The ebeam source accelerating voltage was held at a constant 10 kV throughout the run. A Cr layer was deposited corresponding to approximately 1.0 - 2.0 OD for the initial reflective metallic layer. A second layer of Cr with oxygen streamed into the plume was deposited to generate a CrOx layer atop the Cr metallic layer. Webspeed was held constant at 36 m/min and current was varied from 150 mA to 290 mA in 20 mA increments. The shutter was closed between source current modifications. This process was repeated for 18 m/min and 9 m/min webspeed, with the realization of increasing CrOx thickness from high to low webspeed and low to high ebeam current. In a separate experiment, according to SEM micrographs, a CrOx thickness of approximately 70 - 80 nm corresponds to a strong blue colouration.

[0069] The resulting film varies in colour (from thinnest to thickest CrOx) in the following order: light yellow, orange, burgundy, purple, royal blue, blue, teal, green, green-yellow. Gloss data were collected using a BYK Micro Tri-gloss meter. Additional optical data were collected using a BYK Mac meter. The results of these measurements are summarised in Table 6.

TABLE-US-00007 Optical data for Pre-Examples 5 Current Web Speed Gloss 20° Gloss 60° Flop Index L*.sub.15° L*.sub.45° a*.sub.15° b*.sub.15° control m/min 300 310 26.32 8.31 1 1.19 4.38 150 36 150 306 27.26 10.99 1.54 0.22 4.21 170 36 133 297 24.69 10.17 1.22 0.53 4.98 190 36 84.2 254 33.29 19.65 1.62 1.4 7.69 210 36 45.6 215 35.44 7.9 1.1 1.56 5.73 230 36 44.4 198 26.81 6.83 0.97 1.2 5.78 250 36 46.2 194 130.7 17 1.13 3.51 10.86 270 36 22.9 162 119.53 39.99 0.79 8.93 26.77 290 36 49.3 163 130.2 3.42 0.66 1.85 3.6 150 18 70.8 197 26.06 6.48 1.14 1.93 5.09 170 18 27.7 162 82.34 13.83 0.98 8.5 15.45 190 18 22.5 147 112.41 27.96 1.1 15.81 27.29 210 18 7.4 107 51.74 4.05 0.75 2.68 2.5 230 18 5.3 91 86.52 4.59 0.95 3.58 -0.86 250 18 4.8 70.4 30.98 5.92 1.01 6.05 -8.22 270 18 14.5 69.6 95.66 6.49 1.11 2.89 -10.21 290 18 12.7 69 88.95 5.95 1.4 2.49 -4.93 150 9 91.1 132 28.9 10.91 1.63 -0.94 -6.97 170 9 119 173 29.08 19.33 2.56 -4.14 -9.17 190 9 112 204 39.05 22.2 1.82 -5.44 -7.06 210 9 65.7 199 83.54 39.39 4.11 -7.71 -13.64 230 9 63.4 191 111.15 40.6 4.97 -6.21 -11.62 250 9 84.6 206 86.86 35.08 4.27 -5.98 -4.47 270 9 33.2 138 189.33 59.05 10.19 -6.55 5.14 290 9 41.9 145 94.39 48.87 5.88 -5.38 3.62

Examples 6: 2 Layer Film (Si—Al)

[0070] In a similar set-up as in example 1, 2-layer films were produced with Si as the first semiconducting layer. The ebeam source was positioned 36 cm below the web during process. The ebeam source accelerating voltage was held at a constant 10 kV throughout the run. A Si layer was deposited at a fixed current of 332 mA and webspeed was varied discretely from 6-34 m/s to control Si layer thickness. The shutter was closed between webspeed modifications to signal condition changes during film analysis. Previous silicon depositions using this current setting at 11 m/s webspeed resulted in a Si thickness of 29 +/-2 nm. The expected Si thickness range, therefore, is between 7 nm and 60 nm for the webspeed endpoints of 34 m/s and 6 m/s, respectively. A second layer of metallic Al with thickness corresponding to an optical density of approximately 1.0 - 1.5 OD was deposited atop the Si semiconducting layer.

[0071] The resulting film displays silver coloration on the Al metal side and varies in colour on the Si side from thinnest deposited Si (highest webspeed) to thickest deposited Si (lowest webspeed) in the following order: light yellow, gold, orange, purple, royal blue, blue, teal, teal-green. All films displayed highly reflective visual characteristics with excellent clarity on both silver and coloured sides. Optical colorimetry data were collected using a BYK Mac meter on the coloured film side. The results of these measurements are summarised in Table 7.

TABLE-US-00008 Optical date for Example 6 series Sample Web speed (m/min) Visual Color a*.sub.15° a*.sub.25° a*.sub.45° a*.sub.75° a*.sub.110° b*.sub.15° b*.sub.25° b*.sub.45° b*.sub.75° b*.sub.110° Flop Index Ex. 6a 7 Teal-green -8.00 -3.92 -1.58 -0.73 -0.01 -7.03 -4.93 -1.50 -0.97 -0.76 39.3 Ex. 6b 8 Teal -6.98 -2.78 -0.39 0.25 0.80 -17.01 -9.88 -2.83 -1.31 -0.70 -42.6 Ex. 6c 9 Blue 0.87 1.45 1.15 1.01 1.28 -21.95 -12.38 -3.13 -1.12 -0.51 37.9 Ex. 6d 10 Royal Blue 10.12 5.92 1.99 1.10 1.22 -21.28 -11.83 -2.65 -0.94 -0.48 40.6 Ex. 6e 11 Purple 19.60 10.59 2.77 1.35 1.27 -20.09 -10.84 -2.38 -0.80 -0.42 39.7 Ex. 6f 12 Orange 18.76 10.42 3.55 1.48 1.29 26.11 13.24 3.78 1.46 0.94 40.8 Ex. 6g 14 Orange 16.33 9.08 3.20 1.33 1.15 32.55 16.29 4.47 1.70 0.99 41.2 Ex. 6h 16 Gold 7.61 4.31 1.86 0.99 0.90 40.20 20.67 6.50 2.76 1.62 39.3 Ex. 6i 18 Gold 1.27 2.46 0.93 0.61 0.67 37.84 20.46 6.77 2.58 1.62 38.9 Ex. 6j 21 Gold -2.28 -0.98 -0.72 -0.30 0.17 22.28 12.84 6.46 3.33 2.08 35.9 Ex. 6a 24 Light Gold -2.33 -1.16 -0.90 -0.37 0.16 20.72 11.56 5.77 2.38 1.44 33.8 Ex. 6a 28 Yellow -3.08 -1.62 -1.27 -0.58 0.01 13.95 7.67 4.23 1.75 1.02 33.7 Ex. 6a 32 Light Yellow -3.54 -1.86 -1.29 -0.67 -0.12 11.63 6.80 3.72 1.72 1.27 32.7 Ex. 6a 37 Light Yellow -3.08 -1.56 -1.24 -0.73 -0.15 3.51 1.62 1.02 0.24 0.06 31.6

Example 7: 3-Layer Material (Si—Al—Si)

[0072] In a similar set-up as in example 2, 3-layer materials were produced. The ebeam source was positioned 36 cm below the web during process and webspeed was held at a constant 19 m/min for Si deposition and 11 m/min for Al deposition. The ebeam source accelerating voltage was held at a constant 10 kV throughout the run. In a first step a Si-layer was deposited on a clear polyester film with a release coat layer using PVD ebeam evaporation. Ebeam current was set at the beginning of the run and webspeed was utilized to manipulate the silicon layer thicknesses. In a next step an Al layer was deposited corresponding to approximately 1.0 - 1.5 OD. Optical transmission sensors in combination with current adjustment was utilized to target appropriate Al thickness. In a third process step a further layer of Si was deposited using the same parameters as the first step. Again, ebeam current was set at the beginning of the run to manipulate silicon layer thicknesses. The thickness of the 2 silicon layers was targeted to be the same, so that the webside and metal side of each condition would be the same colour. Si thickness corresponding to yellow and gold was targeted for material 7a and 7b, respectively. Yellow and gold colouration films and subsequent pigments were successfully produced. The colouration of the web and metal side of the films matched well in each material set.

[0073] The materials obtained in Example 7 were all stripped from the polyester film and milled/crushed to a particle size of approximately 14 microns (D50 value). Pigments were prepared with a 10 wt.% in ethanol. Inks were prepared using a total metal content of 3.0 wt-% in a nitrocellulose binder system. The samples were drawn down on a flat BYK drawdown card. Gloss data were collected using a BYK Micro Tri-gloss meter. Additional optical data were collected using a BYK Mac meter. A comparison to Metalure L51010AE (commercially available aluminium PVD pigment from Eckart America) is shown in Table 8, 7c. The results of these measurements are summarised in Table 8.

TABLE-US-00009 Optical data for Examples 7 Sample Gloss 20° Gloss 60° Flop L*15 a*15 a*45 a*110 b*15 b*45 b*110 Visual Color Example 7a 60.5 147 31.57 132.5 -1.46 0.97 1.47 31.41 12.55 10.17 Yellow Example 7b 56.1 142 35.6 127.3 0.31 1.49 2.23 35.89 12.38 9.25 Gold Comparative Example 7c 75.9 170 25.25 139.2 -0.56 0.65 0.45 -0.28 2.86 2.12 Silver