Electrostatic printing

1. A method of printing, comprising:

(a) applying an ink comprising a thermoplastic resin to a print substrate using an electrostatic printing process; and

(b) applying an overcoat composition comprising a crosslinking agent to the ink on the print substrate, such that the thermoplastic resin of the ink is crosslinked;

wherein the crosslinking agent is of formula (I),

(X)—(Y—[Z—F] m ) n    formula (I)

wherein, in each (Y—[Z—F] m ) n , Y, Z, and F are each independently selected, such that F is selected from an aziridine group of the formula —N(CH 2 CR 1 H) or an epoxide of the formula —CH(O)CR 2 H, wherein R 1 and R 2 are selected from H or alkyl; Z is alkylene, and Y is selected from (i) a single bond, —O—, —C(═O)—O—, or —O—C(═O)— where m is 1, or (ii) Y is —NH 2-m , wherein m is 1 or 2, n is at least 1, and X is an organic group.

2. The method according to claim 1 , wherein the thermoplastic resin comprises a polymer having acidic side groups.

3. The method according to claim 1 , wherein the thermoplastic resin comprises a polymer selected from (i) ethylene or propylene acrylic acid co-polymers or (ii) ethylene or propylene methacrylic acid co-polymers.

4. The method according to claim 1 , wherein the crosslinking agent is present in an amount of less than 10 wt % in the overcoat composition.

5. The method according to claim 1 , wherein the crosslinking agent has a molecular weight of 5000 Daltons or less.

6. The method according to claim 1 , wherein the crosslinking agent is or comprises a polyazridine or a polyepoxide.

7. The method according to claim 1 , wherein the crosslinking agent is present in an amount of 6 wt % or less in the overcoat composition.

8. The method according to claim 1 , wherein the crosslinking agent is present in an amount of from 0.5 to 2 wt % in the overcoat composition.

9. The method according to claim 1 , wherein the crosslinking agent has a molecular weight of from 100 to 600 Daltons.