Method for printing on water-soluble material

1. A method for printing on a water-soluble material which comprises the following steps:

A) ink jet printing, using a printer with a single-pass print-head, an ink onto a water-soluble material so as to form an image wherein the ink comprises a self-dispersible pigment which comprises a carboxy-functional dispersant crosslinked around a pigment core by a cross-linking agent having at least two groups selected from oxetane, carbodiimide, hydrazide, oxazoline, aziridine, isocyanate, N-methylol, keteneimine, isocyanurate and epoxy groups;

B) overprinting the image formed in step A) with a water soluble overprint varnish.

2. The method for printing on a water-soluble material according to claim 1 wherein the carboxy-functional dispersant comprises benzyl methacrylate.

3. The method for printing on a water-soluble material as claimed in claim 1 wherein the carboxy-functional dispersant is a copolymer comprising:

(i) from 75 to 97 parts of one or more hydrophobic ethylenically unsaturated monomers comprising at least 50 parts of benzyl methacrylate;

(ii) from 3 to 25 parts of one or more hydrophilic ethylenically unsaturated monomers having one or more carboxy groups; and

(iii) 0 to 1 part of hydrophilic ethylenically unsaturated monomers having one or more hydrophilic non-ionic groups;

wherein the parts are by weight.

4. The method for printing on a water-soluble material as claimed in claim 1 wherein the cross-linking agent has at least two epoxy groups.

5. The method for printing on a water-soluble material as claimed in claim 1 wherein the water-soluble material is a polyvinyl alcohol film.

6. The method for printing on a water-soluble material as claimed in claim 1 wherein in step B) overprinting the image formed in step A) with a water soluble overprint varnish is by flexographic printing.

7. The method for printing on a water-soluble material as claimed in claim 1 wherein in step B) the water-soluble overprint varnish comprises at least one water soluble polymer.

8. The method for printing on a water-soluble material as claimed in claim 7 wherein in step B) the water soluble polymer comprises polyvinyl alcohol.

9. The method for printing on a water-soluble material as claimed in claim 1 which further comprises one or more drying steps.

10. The method for printing on a water-soluble material as claimed in claim 1 comprises the following steps:

i) ink jet printing an ink onto a water-soluble material comprising polyvinyl alcohol so as to form an image wherein the ink comprises a self-dispersible pigment which comprises a carboxy-functional dispersant crosslinked around a pigment core by a cross-linking agent having at least two groups selected from oxetane, carbodiimide, hydrazide, oxazoline, aziridine, isocyanate, N-methylol, keteneimine, isocyanurate and epoxy groups;

ii) drying the image formed in step i);

iii) overprinting the image formed in step ii) with a water soluble overprint varnish comprising polyvinyl alcohol; and

iv) drying the varnished image from step iii).

11. The method for printing on a water-soluble material as claimed in claim 1 wherein step (A) comprises ink-jet printing an ink-set comprising a black ink, a cyan ink, a yellow ink and a magenta ink onto a water soluble material.

12. The method for printing on a water-soluble material as claimed in claim 1 step (A) comprises ink-jet printing an ink-set comprising black ink, red ink, and a white ink wherein the self-dispersing pigments in the black and red inks comprise a carboxy-functional dispersant crosslinked around a pigment core by a cross-linking agent having at least two groups selected from oxetane, carbodiimide, hydrazide, oxazoline, aziridine, isocyanate, N-methylol, keteneimine, isocyanurate and epoxy groups and the white ink comprises titanium dioxide.

13. The method for printing on a water-soluble material as claimed in claim 12 wherein the white ink comprises:

(a) from 1 to 25 parts of titanium dioxide pigment;

(b) from 0 to 8 parts of a styrene butadiene latex binder or styrene acrylic binder;

(c) from 0 to 8 parts of a polyurethane latex binder;

(d) from 0 to 5 parts of a glycol selected from the group consisting of ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol or triethylene glycol;

(e) from 1 to 10 parts of 2-pyrrolidone;

(f) from 1 to 10 parts of glycerol;

(g) from 0.01 to 2 parts of an acetylenic surfactant;

(h) from 0.001 to 5 parts of biocide;

(i) from 0 to 10 parts of polyethylene glycol or polyvinyl alcohol; and

(j) the balance to 100 parts water; provided that (b) plus (c) is greater than 0.