Color laser marking

1. A method for preparing a color laser marked article using three infrared lasers L-1, L-2, and L-3 having respectively a laser emission wavelength of λ(L-1), λ(L-2), and λ(L-3), the method comprising the steps of:

laser marking with the infrared laser L-1 a first color laser markable layer including an infrared dye IR-1 having an absorption maximum λ max (IR-1) in the infrared region and a leuco dye capable of forming a first color;

laser marking with the infrared laser L-2 a second color laser markable layer including an infrared dye IR-2 having an absorption maximum λ max (IR-2) in the infrared region and a leuco dye capable of forming a second color;

laser marking with the infrared laser L-3 a third color laser markable layer including an infrared dye IR-3 having an absorption maximum λ max (IR-3) in the infrared region and a leuco dye capable of forming a third color; and

using a laser or an LED to at least partially expose the color laser marked article to light having a wavelength between 520 nm and 700 nm to at least partially inactivate the infrared dye IR-1, the infrared dye IR-2, and/or the infrared dye IR-3; wherein

the laser emission wavelengths satisfy the condition of:

λ(L-1)>λ(L-2)>λ(L-3);

the infrared red dye absorption maxima satisfy the condition of:

λ max (IR-1)>λ max (IR-2)>λ max (IR-3);

light emitted by the infrared laser L-1 passes, in order, through the third color laser markable layer and the second color laser markable layer before exposing the first color laser markable layer; and

the infrared dye IR-1, the infrared dye IR-2, and the infrared dye IR-3 are cyanine dyes having anions selected from Cl, Br, I, fluoroalkyl sulfonates, arylsulfonates and alkylsulfonates.

2. The method according to claim 1 , wherein the light in the step of at least partially exposing the color laser marked article to light has a wavelength between 550 nm and 600 nm.

3. The method according to claim 1 , wherein 800 nm<λ max (IR-3)<1000 nm.

4. The method according to claim 3 , wherein λ max (IR-1)>1100 nm.

5. The method according to claim 4 , wherein the laser emission wavelengths λ(L-1), λ(L-2), and λ(L-3) differ by no more than 30 nm from the infrared red dye absorption maxima λ max (IR-1), λ max (IR-2), and λ max (IR-3), respectively.

6. The method according to claim 1 , wherein λ max (IR-1)>1100 nm.

7. The method according to claim 1 , wherein the laser emission wavelengths λ(L-1), λ(L-2), and λ(L-3) differ by no more than 30 nm from the infrared red dye absorption maxima λ max (IR-1), λ max (IR-2), and λ max (IR-3), respectively.

8. The method according to claim 1 , wherein the step of at least partially exposing the color laser marked article to light having the wavelength between 520 nm and 700 nm is performed according to an image.

9. The method according to claim 1 , wherein the step of at least partially exposing the color laser marked article to light having the wavelength between 520 nm and 700 nm is an overall exposure.

10. The method according to claim 1 , wherein the color laser marked article is laser marked through a transparent biaxially stretched polyethylene terephthalate foil.

11. The method according to claim 1 , wherein the step of at least partially exposing the color laser marked article to light having the wavelength between 520 nm and 700 nm is performed after the steps of laser marking the first color laser markable layer, laser marking the second color laser markable layer, and laser marking the third color laser markable layer.

12. The method according to claim 1 , wherein the step of at least partially exposing the color laser marked article to light having the wavelength between 520 nm and 700 nm is performed before the step of laser marking the first color laser markable layer, but after the steps of laser marking the second color laser markable layer and laser marking the third color laser markable layer.

13. A method of forming a color laser marked article comprising the steps of:

providing a color laser marked article including, in order, at least:

a) a core support;

b) a first color laser markable layer including an infrared dye IR-1 having an absorption maximum λ max (IR-1) in the infrared region and a leuco dye capable of forming a first color;

c) a second color laser markable layer including an infrared dye IR-2 having an absorption maximum λ max (IR-2) in the infrared region and a leuco dye capable of forming a second color; and

d) a third color laser markable layer including an infrared dye IR-3 having an absorption maximum λ max (IR-3) in the infrared region and a leuco dye capable of forming a third color; and

using a laser or an LED to apply light having a wavelength between 520 nm and 700 nm to the color laser marked article to impede modification by color laser marking of the color laser marked article; wherein

the infrared dye absorption maxima satisfy the condition of:

λ max (IR-1)>λ max (IR-2)>λ max (IR-3); and

the infrared dye IR-1, the infrared dye IR-2, and the infrared dye IR-3 are cyanine dyes having anions selected from Cl, Br, I, fluoroalkyl, sulfonates, arylsulfonates and alkylsulfonates.