Printing system
A printing system is disclosed which comprises an image forming station 12 at which an ink that includes an organic polymeric resin and a coloring agent is applied to an outer surface of an intermediate transfer member 10 to form an ink image, a drying station 14 for drying the ink image to leave a residue film of resin and coloring agent; and an impression station 16 at which the residue film is transferred to a substrate. The intermediate transfer member 10 comprises a thin flexible substantially inextensible belt and the impression station 16 comprises an impression cylinder 20 and a pressure cylinder 18 having a compressible outer surface for urging the belt against the impression cylinder to cause the residue film resting on the outer surface of the belt 10 to be transferred onto a substrate passing between the belt 10 and the impression cylinder 20 during engagement with the pressure cylinder. The belt 10 has a length greater than the circumference of the pressure cylinder 18 and is guided to contact the pressure cylinder over only a portion of its length.
1. A printing system comprising an image forming station at which droplets of an ink that includes an organic polymer resin and a coloring agent in an aqueous carrier are applied to an outer surface of an intermediate transfer member to form an ink image, a drying station for drying the ink image to leave an ink residue film; and an impression station at which the residue film is transferred to a sheet or web substrate wherein the intermediate transfer member comprises a thin flexible endless substantially inextensible belt and wherein the impression station comprises an impression cylinder located outside of the belt and facing an outer surface thereof and a pressure cylinder encircled by the endless belt, the pressure cylinder carrying a compressible blanket mounted around only a portion of the circumference of the pressure cylinder so that opposite ends of the compressible blanket are spaced from one another by a gap, the pressure cylinder being configured to urge the belt against the impression cylinder with sufficient force to cause the residue film resting on the outer surface of the belt to be transferred onto the substrate that passes between the belt and the impression cylinder, the belt having a length greater than the circumference of the pressure cylinder and being guided to contact the pressure cylinder over only a portion of the length of the belt wherein the compressible outer surface of the pressure cylinder causes the outer surface of the belt to conform to the opposing surface of the substrate for an effective transfer of the ink residue film onto the substrate.
2. A printing system as claimed in claim 1 , wherein the belt is driven independently of the pressure cylinder.
3. A printing system as claimed in claim 1 , wherein slack runs of the belt are provided between the impression station and the image forming station to isolate the image forming station from any vibration imposed on the movement of the belt while passing through the impression station.
4. A printing system as claimed in claim 1 , wherein (i) the belt comprises a support layer and a release layer; (ii) the support layer is made of a fabric that is fiber-reinforced at least in the longitudinal direction of the belt, said fiber being a high performance fiber selected from the group comprising aramid, carbon, ceramic, and glass fibers, and (iii) the belt is substantially inextensible in the longitudinal direction of the belt but has limited lateral elasticity to assist in maintaining the belt taut and flat in the image forming station.
5. A printing system as claimed in claim 1 , wherein (i) longitudinally spaced formations, or a thick continuous flexible bead, are/is provided along each of the two lateral edges of the belt, the beads or formations being engaged in lateral guide channels extending at least over the run of the belt passing through the image forming station; and (ii) guide channels are further provided to guide the run of the belt passing through the impression station.
6. A printing system as claimed in claim 5 , wherein the lateral formations are formed by the teeth of one half of a zip fastener sewn, or otherwise secured, to each lateral edge of the belt, through an intermediate lateral elastic strip.
7. A printing system as claimed in claim 1 , wherein the belt is formed by a flat elongate strip of which the ends are secured to one another at a seam to form a continuous loop.
8. A printing system as claimed in claim 1 , wherein a duplexing mechanism is provided for inverting a substrate sheet that has already passed through the impression station and returning the sheet of substrate to pass a second time through the same impression station for an image to be printed onto the reverse side of the substrate sheet.
9. A printing system as claimed in claim 1 , wherein the substrate is a web having no more than half the width of the intermediate transfer member and of the impression station and configured to make a first pass through one side the impression station to receive a printed image on one side and subsequently, after inversion, to make a second pass through the other side of the impression station to receive a printed image on the reverse side.
10. The system of claim 1 wherein: (i) the system is configured to handle and print on substrate sheets so that, at the impression station the residue film is transferred to a substrate sheet of at least a predetermined length; and (ii) the compressible blanket is at least as long as the predetermined length of the substrate sheets.
11. The system of claim 1 wherein the compressible blanket is detachably mounted to the surface of the pressure cylinder.
12. The system of claim 1 further comprising a plurality of rollers mounted on the pressure cylinder within the gap defined by the compressible blanket.
13. A printing system comprising an image forming station at which droplets of an ink that includes an organic polymer resin and a coloring agent in an aqueous carrier are applied to an outer surface of an intermediate transfer member to form an ink image, a drying station for drying the ink image to leave an ink residue film; and an impression station at which the residue film is transferred to a sheet or web substrate wherein the intermediate transfer member comprises a thin flexible endless substantially inextensible belt and wherein the impression station comprises an impression cylinder located outside of the belt and facing an outer surface thereof and a pressure cylinder encircled by the endless belt, the pressure cylinder carrying a compressible blanket that is detachably mounted to the pressure cylinder, the pressure cylinder being configured to urge the belt against the impression cylinder with sufficient force to cause the residue film resting on the outer surface of the belt to be transferred onto the substrate that passes between the belt and the impression cylinder, the belt having a length greater than the circumference of the pressure cylinder and being guided to contact the pressure cylinder over only a portion of the length of the belt wherein the compressible outer surface of the pressure cylinder causes the outer surface of the belt to conform to the opposing surface of the substrate for an effective transfer of the ink residue film onto the substrate.
14. A printing system as claimed in claim 13 , wherein the pressure cylinder comprises a support cylinder and the compressible blanket covers less than the entire circumference of the support cylinder to leave a discontinuity between the ends of the blanket, wherein the impression cylinder has at least one discontinuity for accommodating grippers or vacuum means serving to hold sheets of substrate in position against the impression cylinder, wherein the pressure cylinder and the impression cylinder are rotated in synchronism so that the two discontinuities line up with one another during rotation of the cylinders to leave an enlarged gap between the two cylinders and wherein the belt is driven in such a manner that the seam connecting the ends of the strip forming the belt is timed to pass between the two cylinders of the impression station only when discontinuities in the pressure cylinder and the impression cylinder are aligned with one another.
15. A printing system as claimed in claim 14 , wherein the timing of the passage of the seam between the pressure and impression cylinders is modified by varying the speed of movement of a section of the belt relative to the surface velocity of the pressure and impression cylinders at times when discontinuities in the pressure cylinder and the impression cylinder are aligned with one another.
16. A printing system as claimed in claim 15 , wherein the speed of the belt is varied by providing powered dancers on opposite sides of the nip between the pressure and impression cylinders.
17. A printing system as claimed in claim 14 , wherein, in order to minimize friction between the belt and the pressure cylinder during changing of the phase of the belt, rollers are provided on the pressure cylinder in the discontinuity between the ends of the blanket.
18. The system of claim 13 wherein: (i) the system is configured to handle and print on substrate sheets so that, at the impression station the residue film is transferred to a substrate sheet of at least a predetermined length; and (ii) the compressible blanket is at least as long as the predetermined length of the substrate sheets.
19. A printing system as claimed in claim 13 , wherein the belt is driven independently of the pressure cylinder.
20. A printing system as claimed in claim 13 , wherein slack runs of the belt are provided between the impression station and the image forming station to isolate the image forming station from any vibration imposed on the movement of the belt while passing through the impression station.