Colorant including a mixture of pigments
A colorant including a mixture of pigments is disclosed. The pigments have a similar coloration but different resistance to corrosion. The mixing ratio is selected to optimize the corrosion resistance against color brightness, and/or acidic corrosion resistance against alkali corrosion resistance of the colorant.
1. A colorant comprising:
a mixture of a first pigment P 1 and a second pigment P 2 having chroma C* 1 and C* 2 , respectively, wherein each of C* 1 and C* 2 is at least 10 units in L*a *b* color space under illumination by a D65 standard light source using a 10 degree observer function, wherein a color difference between the first pigment P 1 and the second pigment P 2 is no more than 30 hue degrees in a polar projection of the L*a*b* color space,
wherein the first pigment P 1 undergoes a corrosion-induced color change ΔE*(P 1 ) when immersed into a corrosive solution, and wherein the second pigment P 2 undergoes a corrosion-induced color change ΔE*(P 2 ) when immersed into the corrosive solution, wherein ΔE*(P 2 )<ΔE*(P 1 ),
wherein a corrosion-induced color change ΔE*(P 1 +P 2 ) of the colorant upon immersion into the corrosive solution satisfies a condition ΔE*(P 1 +P 2 )<ΔE*(P 1 ),
wherein the corrosive solution is selected from the group consisting of 2% by weight aqueous solution of H 2 SO 4 , 2% by weight aqueous solution of NaOH, 1.2% by weight aqueous solution of sodium hypochlorite, and water,
wherein the second pigment P 2 includes a plurality of layers,
wherein the plurality of layers include a layer between at least two other layers of the plurality of layers, and
wherein the layer includes FeCr.
2. The colorant of claim 1 , wherein the first pigment P 1 and the second pigment P 2 comprise first and second color-shifting interference pigments, respectively, wherein each of C* 1 and C* 2 and the color difference between the first pigment P 1 and the second pigment P 2 are measured using a d/8° integrating sphere geometry.
3. The colorant of claim 2 , wherein corrosion-induced color changes of the first pigment P 1 and the second pigment P 2 and the colorant comprise base-induced color changes ΔE* B (P 1 ), ΔE* B (P 2 ), and ΔE* B (P 1 +P 2 ), respectively, upon immersion into the 2% by weight aqueous solution of NaOH.
4. The colorant of claim 3 , wherein
the first pigment P 1 undergoes an acid-induced color change ΔE* A (P 1 ) upon immersion into the 2% by weight aqueous solution of H 2 SO 4 , wherein ΔE* A (P 1 )<ΔE* B (P 1 ), and
the second pigment P 2 undergoes an acid-induced color change ΔE* A (P 2 ) upon immersion into the 2% by weight aqueous solution of H 2 SO 4 , wherein ΔE* A (P 2 )>ΔE* B (P 2 ), wherein ΔE* A (P 2 )>ΔE* A (P 1 ), whereby an acid-induced color change ΔE* A (P 1 +P 2 ) of the colorant upon immersion into the 2% by weight aqueous solution of H 2 SO 4 satisfies a condition ΔE* A (P 1 +P 2 )<ΔE* A (P 2 ).
5. The colorant of claim 2 , wherein C* 1 >C* 2 , whereby chroma of the colorant C* c satisfies a condition C* c >C* 2 .
6. The colorant of claim 5 , wherein C* 1 and C* 2 are each at least 15 units in the L*a*b* color space.
7. The colorant of claim 6 , wherein C* 1 and C* 2 are each at least 25 units in the L*a*b* color space.
8. The colorant of claim 1 , wherein a proportion of the first pigment P 1 and the second pigment P 2 in the colorant is between 25:75 and 75:25 by weight.
9. The colorant of claim 2 , wherein ΔE*(P 1 +P 2 )<½ΔE*(P 1 ).
10. The colorant of claim 2 , wherein the color difference between the first pigment P 1 and the second pigment P 2 is no more than 20 hue degrees in the polar projection of the L*a*b* color space.
11. The colorant of claim 2 , wherein the first and second color-shifting interference pigments each comprise a plurality of color-shifting interference flakes having at least five layers including a metal layer, wherein the color-shifting interference flakes of the first color-shifting interference pigment comprise chromium in their outer layers, and the color-shifting interference flakes of the second color-shifting interference pigment comprise bismuth or iron in their outer layers.
12. The colorant of claim 2 , further comprising:
a third pigment P 3 having chroma C* 3 of at least 10 units in the L*a*b* color space under illumination by the D65 standard light source using the 10 degree observer function, wherein a color difference between the first pigment P 1 , the second pigment P 2 , and the third pigment P 3 is no more than 30 hue degrees in a polar projection of the L*a*b* color space,
wherein the third pigment P 3 undergoes a corrosion-induced color change ΔE*(P 3 ) when immersed into the corrosive solution, wherein ΔE*(P3)<ΔE*(P 2 ).
13. A method of manufacture of a colorant, the method comprising:
(a) providing a first pigment P 1 and second pigment P 2 each having chroma C* 1 and C* 2 , respectively, wherein each of C* 1 and C* 2 is at least 10 units in L*a*b* color space under illumination by a D65 standard light source using a 10 degree observer function, wherein a color difference between the first pigment P 1 and the second pigment P 2 is no more than 30 hue degrees in a polar projection of the L*a*b* color space,
wherein the first pigment P 1 undergoes a corrosion-induced color change ΔE*(P 1 ) upon immersion into a corrosive solution, and wherein the second pigment P 2 undergoes a corrosion-induced color change ΔE*(P 2 ) upon immersion into the corrosive solution, wherein ΔE*(P 2 )<ΔE*(P 1 ); and
(b) mixing together the first pigment P 1 and the second pigment P 2 to obtain the colorant having a corrosion-induced color change ΔE*(P 1 +P 2 ) upon immersion into the corrosive solution satisfying a condition ΔE*(P 1 +P 2 )<ΔE*(P 1 ),
wherein the corrosive solution is selected from the group consisting of 2% by weight aqueous solution of H 2 SO 4 , 2% by weight aqueous solution of NaOH, 1.2% by weight aqueous solution of sodium hypochlorite bleach, and water, and
wherein the second pigment P 2 includes a plurality of layers,
wherein the plurality of layers include a layer between at least two other layers of the plurality of layers, and
wherein the layer includes FeCr.
14. The method of claim 13 , wherein in step (a), the first pigment P 1 and second pigment P 2 comprise first and second color-shifting interference pigments, respectively, wherein each of C* 1 and C* 2 and the color difference between the first pigment P 1 and the second pigment P 2 are measured using a d/8° integrating sphere geometry.
15. The method of claim 14 , wherein
in step (a),
corrosion-induced color changes of the first pigment P 1 and the second pigment P 2 and the colorant comprise base-induced color changes ΔE* B (P 1 ), ΔE* B (P 2 ), and ΔE* B (P 1 +P 2 ), respectively, upon immersion into the 2% by weight aqueous solution of NaOH;
the first pigment P 1 undergoes an acid-induced color change ΔE* A (P 1 ) upon immersion into the 2% by weight aqueous solution of H 2 SO 4 , wherein
ΔE* A (P 1 )<ΔE* B (P 1 ); and
the second pigment P 2 undergoes an acid-induced color change ΔE* A (P 2 ) upon immersion into the 2% by weight aqueous solution of H 2 SO 4 , wherein
ΔE* A (P 2 )>ΔE* B (P 2 ), and
ΔE* A (P 2 )>ΔE* A (P 1 ), whereby an acid-induced color change ΔE* A (P 1 +P 2 ) of the colorant upon immersion into the 2% by weight aqueous solution of H 2 SO 4 satisfies a condition ΔE* A (P 1 +P 2 )<ΔE* A (P 2 ).
16. The method of claim 15 , wherein in step (a), the first color-shifting interference pigment comprises a plurality of multi-layer color-shifting interference flakes having chromium in outer layers thereof, and the second color-shifting interference pigment comprises a plurality of multi-layer color-shifting interference flakes having bismuth or iron in outer layers thereof.
17. The method of claim 14 , wherein
step (b) includes mixing in a third pigment P 3 having chroma C* 3 of at least 10 units in the L*a*b* color space under illumination by the D65 standard light source using a 10 degree observer function,
a color difference between the first pigment P 1 , the second pigment P 2 , and the third pigment P 3 is no more than 30 hue degrees in a polar projection of the L*a*b* color space, and
the third pigment P 3 undergoes a corrosion-induced color change ΔE*(P 3 ) when immersed into the corrosive solution, wherein ΔE*(P 3 )<ΔE*(P 2 ).
18. A colorant comprising a mixture of a first pigment P 1 and a second pigment P 2 ,
wherein the first pigment P 1 is Cr/MgF 2 /Al/MgF 2 /Cr,
wherein the second pigment P 2 includes a plurality of layers,
wherein the plurality of layers include a layer between at least two other layers of the plurality of layers, and
wherein the layer includes FeCr.
19. A colorant comprising a mixture of a first pigment P 1 and a second pigment P 2 wherein P 1 is Cr/MgF 2 /Al/MgF 2 /Cr and P 2 is Bi/MgF 2 /FeCr/MgF 2 /Bi.
20. A colorant comprising a mixture of a first pigment P 1 and a second pigment P 2 wherein P 1 is Cr/MgF 2 /Al/MgF 2 /Cr and P 2 is Fe/MgF 2 /FeCr/MgF 2 /Fe.