Ink film constructions
An ink film construction including: (a) a printing substrate; and (b) at least one ink film, fixedly adhered to a top surface of the printing substrate, the ink film having an upper film surface distal to the top surface of the substrate, wherein a surface concentration of nitrogen at the upper film surface exceeds a bulk concentration of nitrogen within the film, the bulk concentration measured at a depth of at least 30 nanometers below the upper film surface, and wherein a ratio of the surface concentration to the bulk concentration is at least 1.1 to 1.
1. A method for preparing an ink dot construction which ink dot construction comprises:
(a) a fibrous printing substrate selected from the group consisting of an uncoated fibrous printing substrate and a commodity coated fibrous printing substrate; and
(b) a plurality of ink dots, each ink dot of said ink dots fixedly adhered to a top substrate surface of said fibrous printing substrate, said ink dots containing at least one colorant dispersed in an organic polymeric resin, each said ink dot covering a continuous area of said top substrate surface;
each said ink dot being disposed entirely above said continuous area, such that a projected perpendicular line, extending down towards said top substrate surface, first meets said ink dot, before meeting said top substrate surface, at every point in said continuous area;
each said ink dot having a diameter of 15 to 300 micrometers;
each of said ink dots being characterized by a dimensionless aspect ratio (R aspect ) defined by:
R aspect =D dot /H dot
wherein D dot is said diameter; and H dot is said average thickness;
said aspect ratio being at least 50,
each of said ink dots having an average or characteristic thickness of at most 1,800 nm;
the method comprising:
(iii) depositing onto a silicone release layer of an intermediate transfer member of a printing system, via a plurality of ink-jet printing heads, a plurality of droplets of a water-based ink formulation, the depositing being conducted such that each droplet spreads on impinging upon the intermediate transfer member to form a flattened liquid ink droplet, whereby to form a plurality of flattened liquid ink droplets;
(iv) heating the flattened liquid ink droplets sufficiently rapidly so as to dry them sufficiently to prevent their beading on said release layer and to produce a residue film;
(v) transferring the residue film from the silicone release layer to said substrate;
wherein said water-based ink formulation comprises (a) a solvent containing water and, optionally, a co-solvent, said water constituting at least 8 wt. % of the formulation; (b) at least one colorant dispersed or at least partly dissolved within said solvent, said colorant constituting at least 1 wt. % of the formulation; and (c) an organic polymeric resin having an average molecular weight of at least 8,000 which is dispersed or at least partially dissolved within said solvent, the resin constituting 6 to 40 wt. % of the formulation,
the ink formulation being characterized in that the weight ratio of the resin to the colorant is at least 1.5:1.
2. The method of claim 1 , further comprising, before said depositing,
(i) applying to said silicone release layer an aqueous solution or dispersion of a polymeric chemical agent which reduces the hydrophobic effect of the silicone layer, the chemical agent having at least one of (a) a positive charge density of at least 3 meq/g of chemical agent and an average molecular weight of at least 5,000, (b) a positive charge density of at least 6 meq/g of chemical agent and an average molecular weight of at least 1,000, (c) a nitrogen content of at least 1 wt. % and an average molecular weight of at least 50,000, and (d) a nitrogen content of at least 18 wt. % and an average molecular weight of at least 10,000; and
(ii) removing the aqueous solvent of said chemical agent.
3. A method for preparing an ink dot construction which ink dot construction comprises:
(a) a fibrous printing substrate selected from the group consisting of an uncoated fibrous printing substrate and a commodity coated fibrous printing substrate; and
(b) a plurality of ink dots, each ink dot of said ink dots fixedly adhered to a top substrate surface of said fibrous printing substrate, said ink dots containing at least one colorant dispersed in an organic polymeric resin, each said ink dot covering a continuous area of said top substrate surface;
each said ink dot being disposed entirely above said continuous area, such that a projected perpendicular line, extending down towards said top substrate surface, first meets said ink dot, before meeting said top substrate surface, at every point in said continuous area;
each said ink dot having a diameter of 15 to 300 micrometers;
each of said ink dots being characterized by a dimensionless aspect ratio (R aspect ) defined by:
R aspect =D dot /H dot
wherein D dot is said diameter; and H dot is said average thickness;
said aspect ratio being at least 50,
each of said ink dots having an average or characteristic thickness of at most 1,800 nm;
the method comprising:
(iii) depositing onto a silicone release layer of an intermediate transfer member of a printing system, via a plurality of ink-jet printing heads, a plurality of droplets of a water-based ink formulation, the depositing being conducted such that each droplet spreads on impinging upon the intermediate transfer member to form a flattened liquid ink droplet, whereby to form a plurality of flattened liquid ink droplets;
(iv) heating the ink films sufficiently rapidly so as to dry them sufficiently to prevent their beading on said release layer and to produce a residue film; and
(v) transferring the residue film from the silicone release layer to said substrate;
wherein said water-based ink formulation comprises (a) a solvent containing water and, optionally, a co-solvent, said water constituting at least 8 wt. % of the formulation; (b) at least one colorant dispersed or at least partly dissolved within said solvent, said colorant constituting at least 1 wt. % of the formulation; and (c) an organic polymeric resin having an average molecular weight of at least 8,000 which is dispersed or at least partially dissolved within said solvent, the resin constituting 6 to 40 wt. % of the formulation,
the ink formulation being characterized in that is has at least one of (i) a viscosity of 2 to 25 cP at at least one temperature in the range of 20-60° C. and (ii) a surface tension of not more than 50 milliNewton/m at at least one temperature in the range of 20-60° C.
4. The method of claim 3 , further comprising, before said depositing,
(i) applying to said silicone release layer an aqueous solution or dispersion of a polymeric chemical agent which reduces the hydrophobic effect of the silicone layer, the chemical agent having at least one of (a) a positive charge density of at least 3 meq/g of chemical agent and an average molecular weight of at least 5,000, (b) a positive charge density of at least 6 meq/g of chemical agent and an average molecular weight of at least 1,000, (c) a nitrogen content of at least 1 wt. % and an average molecular weight of at least 50,000, and (d) a nitrogen content of at least 18 wt. % and an average molecular weight of at least 10,000; and
(ii) removing the aqueous solvent of said chemical agent.
5. The method of claim 2 , wherein said colorant comprises a pigment or mixture of pigment, at least one said pigment having an average particle size (D 50 ) in the range of from 20 to 120 nm inclusive.
6. The method of claim 2 wherein the ink is such that, when substantially dried, (a) at at least one temperature in the range of 90° C. to 195° C., the dried ink has a first dynamic viscosity in the range of 1,000,000 (1×10 6 ) cP to 300,000,000 (3×10 8 ) cP, and (b) at at least one temperature in the range of 50° C. to 85° C., the dried ink has a second dynamic viscosity of at least 80,000,000 (8×10 7 ) cP, wherein the second dynamic viscosity exceeds the first dynamic viscosity.
7. The method of claim 2 , wherein the polymeric resin is an acrylic-based polymer selected from an acrylic polymer and an acrylic-styrene copolymer.
8. The method of claim 2 , wherein the ink formulation further comprises a surfactant, in addition to the polymeric resin, colorant, water and optional co-solvent, said surfactant being present in an amount of not more than 2 wt. %.
9. The method of claim 2 , wherein the ink formulation, when substantially dried, has a T g of at most 50° C.
10. The method of claim 2 , wherein said heating comprises first heating the flattened liquid ink droplets sufficiently rapidly so as to dry them sufficiently to prevent their beading on said release layer, and further heating them to produce a residue film.
11. The method of claim 2 , wherein after removing the solvent from said chemical agent, said chemical agent forms a coating of not more than 300 nm thickness on said release layer.
12. The method of claim 11 , wherein the ratio of charges in the ink droplets to the charges in the chemical agent in the region covered by said ink droplets is at least 2:1.
13. The method of claim 12 , wherein the charge density of the chemical agent is at least 6 meq/g.
14. The method of claim 13 , wherein the charge density of said coating is at least 12 meq/m 2 .
15. The method of claim 4 , wherein at least a portion of said plurality of ink dots constitutes an ink dot set contained within a square geometric projection projecting on said first printing substrate, said ink dot set containing at least 10 distinct ink dots, fixedly adhered to a surface of said first printing substrate, all said ink dots within said square geometric projection being counted as individual members of said set, each of said ink dots containing at least one colorant dispersed in an organic polymeric resin, each of said dots having an average thickness of less than 2,000 nm, and a diameter of 5 to 300 micrometers;
each ink dot of said ink dots having a generally convex shape in which a deviation from convexity, (DC dot ), is defined by:
DC dot =1− AA/CSA,
AA being a calculated projected area of said dot, said area disposed generally parallel to said first fibrous printing substrate; and
CSA being a surface area of a convex shape that minimally bounds a contour of said projected area;
wherein a mean deviation from convexity (DC dot mean ) of said ink dot set is at most 0.05.