Ink formulations and film constructions thereof

1. A method of indirect printing comprising:

a. providing a water-based ink formulation comprising:

(i) a solvent containing water;

(ii) at least one colorant dispersed or at least partly dissolved within the solvent;

(iii) at least one organic polymeric resin, dispersed within the solvent; and

(iv) a softening agent selected to reduce a glass transition temperature (T g ) Of said polymeric resin,

wherein the ink formulation provides all of a first feature, a second feature, a third feature, a fourth feature, and a fifth feature, said first through fifth features being defined below;

b. directing droplets of the ink formulation onto an intermediate transfer member (ITM) having a hydrophobic outer surface so as to form an ink image thereon;

c. subjecting the ink image, on the hydrophobic outer surface of the ITM, to a heating-and-drying process so as to obtain an ink film;

d. subjecting the ITM outer surface to pressurized contact with substrate so as to transfer the ink film thereto,

wherein the first, second, third, fourth, and fifth features are defined as follows:

i. according to the first feature, the ink formulation is either devoid of inorganic filler particles or has an inorganic filler particle concentration of less than 0.1 wt. %;

ii. according to the second feature, the ink formulation forms, when dried, a substantially dry ink residue having:

(A) a first dynamic viscosity within a range of 10 6 cP to 3·10 8 cP over at least part of a first temperature range of 60° C. to 110° C.; and

(B) a second dynamic viscosity of at least 6·10 7 cP, over at least a part of a second temperature range of 50° C. to 55° C.;

said second dynamic viscosity at 55° C. exceeding the first dynamic viscosity at 85° C.;

iii. according to the third feature, said softening agent has a pure vapor pressure of at most 0.40 kPa at 150° C.;

iv. according to the third feature, at least one particular resin of said organic polymeric resin having an elevated glass transition temperature (T g ) of at least 54° C.; and

v. according to the fifth feature, said softening agent is selected and/or added in an amount to reduce said elevated glass transition temperature by at least 5° C.

2. The method of claim 1 wherein a thickness of the ink film is at most 300 nm.

3. The method of claim 1 wherein the ink formulation is devoid of inorganic filler particles.

4. The method of claim 1 wherein the method is performed such that the heating-and-drying process renders the ink film tacky.

5. The method of claim 1 wherein the method is performed such that immediately before transfer to substrate, the ink film is substantially dry.

6. The method of claim 1 , wherein a weight ratio of said organic polymeric resin to said colorant is at least 3.5:1.

7. The method of claim 6 , wherein said weight ratio of said organic polymeric resin to said colorant is at least 4:1.

8. The method of claim 1 , wherein said elevated glass transition temperature (T g ) is at least 56° C.

9. The method of claim 1 , wherein said elevated glass transition temperature (T g ) is at least 60° C.

10. The method of claim 1 , wherein said softening agent is selected and/or added in an amount to reduce said elevated glass transition temperature by at least 7° C.

11. The method of claim 1 , wherein said softening agent is selected and/or added in an amount to reduce said elevated glass transition temperature by at least 10° C.

12. The method of claim 1 , wherein said softening agent is selected and/or added in an amount to reduce said elevated glass transition temperature by at least 15° C.

13. The method of claim 1 , wherein the formulation is an aqueous inkjet ink having at least one of:

(i) a viscosity of 2 to 25 cP at at least one particular temperature in a jetting temperature range of 20-60° C.; and

(ii) a surface tension of at most 50 milliNewton/m at at least one particular temperature within said jetting temperature range.

14. The method of claim 1 , wherein ΔT defines a temperature differential between a temperature (T F ) at which said dried ink residue begins to exhibit a particular degree of flowability, and a baseline temperature (T B ):

Δ T=T F −T B

said degree of flowability being defined by a critical viscosity (μ CR ) at which said degree of flowability is achieved,

and wherein, when said baseline temperature equals 50° C., and said critical viscosity equals 10 8 cP, said temperature differential is at least 3° C.

15. The method of claim 1 , said polymeric resin including, mainly including, or consisting essentially of an acrylic-based polymer selected from the group consisting of an acrylic polymer and an acrylic-styrene copolymer.