Security devices incorporating colour shifting inks

1. A security document or device including at least one area formed from a transparent plastics material which is exposed on at least one side to form a window or half-window, and a first colour shifting ink composition including a first interference pigment and a first colour pigment and a second colour shifting ink composition including a second interference pigment and a second colour pigment, applied in at least part of the window or half-window, wherein the first colour shifting ink composition provides, at a first viewing angle, a first colour from the first interference pigment and the second colour shifting ink composition provides, at the first viewing angle, substantially the same first colour from the second interference pigment, wherein, at a second viewing angle, different from the first viewing angle, the first colour shifting ink composition provides a second colour from the first colour pigment and the second colour shifting ink composition provides a third colour from the second colour pigment, different from the first and second colour, wherein the first and second interference pigment are different than one another and the first and second organic colour pigments are different than one another.

2. A security document or device as claimed in claim 1 including a transparent plastics substrate, and at least one opacifying coating applied to a surface on at least one side of the substrate in such a manner as to leave a region of the substrate uncovered to form the window or half-window.

3. A security document or device as claimed in claim 1 including a third colour shifting ink composition, wherein the third colour shifting ink composition has an interference pigment which provides a fourth colour at the first viewing angle, different to the first colour provided by the first and second colour shifting ink composition, and a colour pigment which provides the second or third colour at the second viewing angle, as provided by the first or second colour shifting ink composition.

4. A security document or device as claimed in claim 1 , wherein at least one of the first, second or third colour shifting ink compositions includes an anti-stokes material, wherein the anti-stokes material is chosen to enable identification on the colour shifting ink composition and/or security document or device.

5. A security document including a security device as claimed in claim 1 , wherein the security document is one of the following: an item of currency such as a banknote or coin, a credit card, a cheque, a passport, an identity card, a security or share certificate, a driver's licence, a deed of title, a travel document, such as an airline or train ticket, an entrance card or ticket, a birth, death or marriage certificate, and an academic transcript.

6. A method of producing a security document or device which includes the steps of:

providing a sheet-like substrate of transparent plastics material having first and second surfaces on opposite sides of the substrate;

applying at least one opacifying coating on said first surface of the substrate in such a manner as to leave a region of the substrate uncovered to form a window;

applying a first colour shifting ink composition including a first colour pigment and a first interference pigment in at least part of the window region of the substrate; and

applying a second colour shifting ink composition including a second colour pigment and a second interference pigment in at least part of the window region of the substrate,

wherein the first colour shifting ink composition provides, at a first viewing angle, a first colour from the first interference pigment and the second colour shifting ink composition provides, at the first viewing angle, substantially the same first colour from the second interference pigment, wherein at a second viewing angle, different from the first viewing angle, the first colour shifting ink composition provides a second colour from the first colour pigment and the second colour shifting ink composition provides a third colour from the second colour pigment, different from the first and second colour, wherein the first and second interference pigment are different than one another and the first and second organic colour pigments are different than one another.

7. A method as claimed in claim 6 , including applying a third colour shifting ink composition having a third interference pigment which provides a fourth colour at the first viewing angle, different to the first colour provided by the first and second colour shifting ink composition, and a colour pigment which provides the second or third colour at the second viewing angle, as provided by the first or second colour shifting ink composition.

8. A method as claimed in claim 6 , including adding an anti-stokes material to at least one of the first, second or third colour shifting ink compositions includes, wherein the anti-stokes material is chosen to enable identification on the colour shifting ink composition and/or security document or device.

9. A security document or device including at least one area formed from a transparent plastics material which is exposed on at least one side to form a window or half-window, and a first colour shifting ink composition including a first interference pigment and a first organic colour pigment and a second colour shifting ink composition including a second interference pigment and a second organic colour pigment, applied in at least part of the window or half-window, wherein the first colour shifting ink composition provides, at a first viewing angle, a first colour from the first interference pigment and the second colour shifting ink composition provides, at the first viewing angle, substantially the same first colour from the second interference pigment, wherein, at a second viewing angle, different from the first viewing angle, the first colour shifting ink composition provides a second colour from the first organic colour pigment and the second colour shifting ink composition provides a third colour from the second organic colour pigment, different from the first and second colour, wherein the first and second interference pigment are different than one another and the first and second organic colour pigments are different than one another.