Digital printing process

1. A method of printing comprising:

a. providing an intermediate transfer member (ITM) comprising a silicone-based release layer surface that is sufficiently hydrophilic to satisfy at least one of the following properties: (i) a receding contact angle of a drop of distilled water deposited on the silicone-based release layer surface is at most 60°; and (ii) a 10-second dynamic contact angle (DCA) of a drop of distilled water deposited on the silicone-based release layer surface is at most 108°;

b. providing an aqueous treatment formulation comprising:

i. at least 1.5%, by weight, of a quaternary ammonium salt having a solubility in water, at 25° C., of at least 5%;

ii. at least 1%, by weight, of at least one water soluble polymer having a solubility in water of at least 5% at 25° C.; and

iii. a carrier liquid containing water, said water making up at least 65%, by weight of the aqueous treatment formulation;

 the aqueous treatment formulation having the following properties:

i. a static surface tension within a range of 20 and 40 dynes/cm at 25° C.;

ii. a 25° C. dynamic viscosity that is at least 10 cP; and

iii. a 60° C. evaporation load of at most 8:1, by weight;

c. applying the aqueous treatment formulation to the silicone-based release layer surface of the ITM to form thereon a wet treatment layer having a thickness of at most 0.8 μm;

d. subjecting the wet treatment layer to a drying process to form a dried treatment film, from the wet treatment layer, on the silicone-based release layer surface;

e. depositing droplets of an aqueous ink onto the dried treatment film to form an ink image on the release layer surface of the silicone-based release layer surface;

f. drying the ink image to leave an ink-image residue on the silicone-based release layer surface; and

g. transferring the ink-image residue onto a printing substrate by pressured contact between the ITM and the printing substrate.

2. The method of claim 1 , wherein the 60° C. evaporation load of the provided aqueous treatment formulation is at most 6:1, at most 5:1, at most 4:1, at most 3.5:1, or at most 3:1, and optionally, at least 2:1, at least 2.2:1 or at least 2.5:1.

3. The method of claim 1 , wherein a concentration of said quaternary ammonium salt within the provided aqueous treatment formulation is within a range of 1.5% to 15%; a concentration of said water soluble polymer is within a range of 2.5 to 10% or 2.5 to 8%, a 60° C. evaporation load is within a range of 2.5:1 to 4:1, and said viscosity is at least 12 cP, and optionally, at least 14 cP or at least 16 cP.

4. The method of claim 1 , wherein the provided aqueous treatment formulation has a total surfactant concentration of at least 6%, at least 7%, at least 8%, at least 9%, or at least 10%, and optionally, within a range of 6 to 40%, 6 to 30%, 6 to 20%, 7 to 30%, 7 to 20%, 7 to 15%, 8 to 25%, 8 to 20%, 8 to 15%, or 8 to 13%.

5. The method of claim 1 , wherein the quaternary ammonium salt of the provided aqueous treatment formulation is an organic quaternary ammonium salt.

6. The method of claim 1 wherein the silicone-based release layer surface is sufficiently hydrophilic to satisfy at least one of the following property: a receding contact angle of a drop of distilled water deposited on the silicone-based release layer surface is at most 60°.

7. The method of claim 1 wherein the silicone-based release layer surface is sufficiently hydrophilic to satisfy at least one of the following property: a 10-second dynamic contact angle (DCA) of a drop of distilled water deposited on the silicone-based release layer surface is at most 108°.

8. The method of claim 1 , wherein the provided ITM comprises a support layer and a release layer having said silicone-based release layer surface and a second surface that (i) opposes said silicone-based release layer surface, and (ii) is attached to said support layer, and wherein said release layer is formed of an addition-cured silicone material.

9. The method of claim 1 , wherein a surface hydrophobicity of silicone-based release layer surface of the provided ITM is less than a bulk hydrophobicity of the cured silicone material within the release layer, the surface hydrophobicity being characterized by a receding contact angle of a droplet of distilled water on the ink reception surface, the bulk hydrophobicity being characterized by a receding contact angle of a droplet of distilled water disposed on an inner surface formed by exposing an area of the cured silicone material within the release layer to form an exposed area.

10. The method of claim 1 , wherein the aqueous treatment formulation is applied to the silicone-based release layer surface such that the thickness of the wet treatment layer is at most 0.5 μm or at most 0.4 μm.

11. The method of claim 1 , wherein formation of the wet treatment layer or thinning thereof comprises forcing the aqueous treatment formulation to flow such that a velocity gradient normal to the ITM is established, a magnitude of the velocity gradient being at least 10 6 sec −1 or at least 2×10 6 sec −1 .

12. The method of claim 1 , wherein the drying of the treatment solution is performed sufficiently rapidly so as to prevent beading and so as leave a continuous hydrophilic and cohesive polymer treatment film having a thickness of at most 200 nm, or at most 150 nm, or at most 120 nm, or at most 100 nm, or at most 80 nm, or at most 70 nm, or at most 60 nm, or at most 50 nm, or at most 40 nm, or at most 30 nm.

13. The method of claim 1 , wherein a thickness of the dried treatment film to which the aqueous ink droplets are deposited is at most 200 nm, or at most 120 nm, or at most 100 nm, or at most 80 nm.

14. The method of claim 1 , wherein a thickness of the dried treatment film to which the aqueous ink droplets are deposited is at least 15 nm or at least 20 nm or at least 30 nm.

15. The method of claim 1 , wherein the dried treatment film is continuous over an entirety of a rectangle of the release surface of the ITM, wherein said rectangle has a width of at least 10 cm and a length of at least 10 meters.

16. The method of claim 1 , wherein the ink-image residue is transferred together with non-printed areas of the dried treatment film onto the printing substrate.

17. The method of claim 16 wherein a thickness of the dried treatment film is at most 120 nm.

18. The method of claim 1 , wherein the dried treatment film is sufficiently cohesive such that during transfer of the ink-image residue, the dried treatment film completely separates from the ITM and transfers to the printing substrate with the dried ink image, both in printed and non-printed areas.

19. The method of claim 1 wherein the aqueous treatment formulation comprises at least 3%, by weight, of a quaternary ammonium salt having a solubility in water, at 25° C., of at least 5%.

20. A printing system comprising:

a. an intermediate transfer member (ITM) comprising a silicone-based release layer surface that is sufficiently hydrophilic to satisfy at least one of the following properties: (i) a receding contact angle of a drop of distilled water deposited on the silicone-based release layer surface is at most 60°; and (ii) a 10-second dynamic contact angle (DCA) of a drop of distilled water deposited on the silicone-based release layer surface is at most 108°;

b. a quantity of an aqueous treatment formulation comprising:

i. at least 1.5%, by weight, of a quaternary ammonium salt having a solubility in water, at 25° C., of at least 5%;

ii. at least 1%, by weight, of at least one water soluble polymer having a solubility in water of at least 5% at 25° C.; and

iii. a carrier liquid containing water, said water making up at least 65%, by weight of the aqueous treatment formulation;

 the aqueous treatment formulation having the following properties:

i. a static surface tension within a range of 20 and 40 dynes/cm at 25° C.;

ii. a 25° C. dynamic viscosity that is at least 10 cP; and

iii. a 60° C. evaporation load of at most 8:1, by weight;

c. a treatment station for applying the aqueous treatment formulation to the silicone-based release layer surface of the ITM to form thereon a wet treatment layer having a thickness of at most 0.8 μm;

d. means for subjecting the wet treatment layer to a drying process to form a dried treatment film, from the wet treatment layer, on the silicone-based release layer surface;

e. an image forming station for depositing droplets of an aqueous ink onto the dried treatment film to form an ink image on the release layer surface of the silicone-based release layer surface;

f. a drying station for drying the ink image to leave an ink-image residue on the silicone-based release layer surface; and

g. an impression station for transferring the ink-image residue onto a printing substrate by pressured contact between the ITM and the printing substrate.