Electrostatic ink compositions, methods and print substrates

1. An electrostatic ink composition comprising

a liquid carrier;

chargeable particles comprising

a co-polymer of an alkylene monomer and an acrylic acid monomer, and

a pearlescent, non-metallic pigment;

a charge director; and

a charge adjuvant,

wherein the chargeable particles are dispersed in the liquid carrier,

wherein the pearlescent, non-metallic pigment has an aspect ratio of a diameter measured in a direction perpendicular to the thickness to its thickness of n:1, where n is at least 2 and n is 100 or less, and

wherein the w/w ratio of the copolymer of an alkylene monomer and an acrylic acid monomer to the pearlescent, non-metallic pigment is from 10:1 to 4:1.

2. An electrostatic ink composition according to claim 1 , wherein the pearlescent, non-metallic pigment comprises flakes comprising a material selected from mica having on one or more surfaces thereof a high refractive index metal compound.

3. An electrostatic ink composition according to claim 2 , wherein the high refractive index metal compound is selected from titanium oxide and an iron oxide.

4. An electrostatic ink composition according to claim 1 , wherein the pearlescent, non-metallic pigment comprises flakes having a diameter of from 1 μm to 50 μm.

5. An electrostatic ink composition according to claim 1 , wherein the chargeable particles further comprise a salt of multivalent cation and a fatty acid anion.

6. An electrostatic ink composition according to claim 5 , wherein the multivalent cation is Al 3+ .

7. An electrostatic ink composition according to claim 5 , wherein the composition further comprises a charge director selected from metal salts of sulfo-succinates, metal salts of oxyphosphates, metal salts of alkyl-benzenesulfonic acid, metal salts of aromatic carboxylic acids or sulfonic acids, as well as zwitterionic and non-ionic compounds, such as polyoxyethylated alkylamines, lecithin, polyvinylpyrrolidone, and organic acid esters of polyvalent alcohols.

8. An electrostatic ink composition according to claim 1 , wherein the alkylene monomer is selected from ethylene and propylene and the acrylic acid monomer is selected from acrylic acid and methacrylic acid.

9. An electrostatic ink composition according to claim 1 , wherein the chargeable particles have been formed by grinding of the co-polymer of an alkylene monomer and an acrylic acid monomer, and the pearlescent, non-metallic pigment in the presence of a salt of multivalent cation and a fatty acid anion.

10. A method of electrophotographic printing an electrostatic ink composition, wherein the ink composition comprises

a liquid carrier; and

chargeable particles comprising

a co-polymer of an alkylene monomer and an acrylic acid monomer, and

a pearlescent, non-metallic pigment,

wherein the chargeable particles are dispersed in the liquid carrier,

wherein the pearlescent, non-metallic pigment has an aspect ratio of a diameter measured in a direction perpendicular to the thickness to its thickness of n:1, where n is at least 2 and n is 100 or less, and

wherein the w/w ratio of the copolymer of an alkylene monomer and an acrylic acid monomer to the pearlescent, non-metallic pigment is from 10:1 to 4:1;

a charge director; and

a charge adjuvant,

the method comprising:

forming a latent electrostatic image on a surface;

contacting the surface with the electrostatic ink composition, such that at least some of the chargeable particles adhere to the surface to form a developed toner image on the surface, and

transferring the toner image to a print substrate.

11. A method according to claim 10 , wherein, before being passed to the latent electrostatic image on the surface, the electrostatic ink composition is first passed between an electrode and a developer roller, then passed on the developer roller by a squeegee roller, before being transferred to the surface, wherein electrode voltage is set at from 1600 to 1800 V, the developer roller voltage is set at from 400 to 600 V and the squeegee roller is set at from 800 to 1000 V.

12. A print substrate having printed thereon an ink comprising

a co-polymer of an alkylene monomer and an acrylic acid monomer, and

a pearlescent, non-metallic pigment,

a charge director, and

a charge adjuvant,

wherein the pearlescent, non-metallic pigment has an aspect ratio of a diameter measured in a direction perpendicular to the thickness to its thickness of n:1, where n is at least 2 and n is 100 or less, and

wherein the w/w ratio of the copolymer of an alkylene monomer and an acrylic acid monomer to the pearlescent, non-metallic pigment is from 10:1 to 4:1.

13. A print substrate according to claim 12 , wherein the pearlescent, non-metallic pigment comprises flakes comprising a material selected from mica having on one or more surfaces thereof a high refractive index metal compound.