Image transfer for liquid electro-photographic printing
View Patent ↗In one example, an LEP printer includes a belt rotatable in a loop, a series of multiple printing units along the belt each to apply an LEP ink color separation to the belt, a first heater to dry the color separations on the belt to a molten film at a drying temperature, a second heater to heat the molten film on the belt to a transfer temperature higher than the drying temperature, and a pressure roller near the belt to press a printable substrate against the belt at a nip between the pressure roller and the belt.
1 . An LEP printer comprising:
a belt rotatable in a loop;
a series of multiple LEP printing units along the belt each to apply an LEP ink color separation to the belt;
a first heater to dry the color separations on the belt to a molten film at a drying temperature;
a second heater to heat the molten film on the belt to a transfer temperature higher than the drying temperature by a beam of light having an exposure time of 2 to 3 milliseconds; and
a pressure roller near the belt to press a printable substrate against the belt at a nip between the pressure roller and the belt, wherein the second heater is located before the pressure roller.
2 . The printer of claim 1 , wherein:
the first heater comprises a series of multiple first heaters along the belt, each first heater having a first intensity; and
the second heater comprises a laser having a second intensity greater than the first intensity.
3 . The printer of claim 2 , wherein the second heater is located along the belt such that, when the belt is rotating, the molten film enters the nip within 30 ms after the second heater heats the molten film to the transfer temperature.
4 . The printer of claim 3 , wherein the second intensity is at least 1.0 W/mm 2 .
5 . The printer of claim 4 , wherein:
the drying temperature is 90° C.-110° C.; and
the transfer temperature is 120° C.-160° C.
6 . The printer of claim 5 , wherein:
one or more of the first heaters is located between each pair of adjacent printing units; and
one or more of the first heaters is located downstream from all of the printing units.
7 . An LEP printer, comprising:
a belt rotatable in a loop;
a series of multiple printing units along the belt each to apply an LEP ink color separation to the belt;
a series of multiple first heaters along the belt, each first heater having a first intensity to dry the color separations on the belt to a molten film at a drying temperature;
a second heater having a second intensity greater than the first intensity to heat the molten film on the belt to a transfer temperature higher than the drying temperature;
a pressure roller near the belt to press a printable substrate against the belt at a nip between the pressure roller and the belt; and
a controller programmed to: rotate the belt; and turn off some of the first heaters based on a density of the color separations on the belt.
8 . The printer of claim 7 , wherein:
one or more of the first heaters is located between each pair of adjacent printing units; and
one or more of the first heaters is located downstream from all of the printing units.
9 . The printer of claim 7 , wherein the second heater is located along the belt such that the molten film enters the nip within 30 ms after the second heater heats the molten film to the transfer temperature.
10 . The printer of claim 7 , wherein the second intensity is at least 1.0 W/mm 2 .
11 . An LEP printing process, comprising:
rotating an intermediate transfer belt in a loop; and
during a single rotation of the belt loop:
gathering multiple LEP ink color separations together on the rotating belt;
drying the color separations on the rotating belt to a molten film at a drying temperature;
then heating the molten film on the rotating belt to a transfer temperature greater than the drying temperature by a beam of light having an exposure time of 2 to 3 milliseconds; and
within 30 ms after heating the film on the rotating belt to the transfer temperature, transferring the film from the rotating belt to a printable substrate, wherein the heating is performed at a location on the intermediate transfer belt before the transferring.
12 . The process of claim 11 , wherein:
drying the color separations comprises heating the color separations with a first heater having a first intensity; and
heating the molten film comprises heating the molten film with a second heater comprising a laser having a second intensity greater than the first intensity.
13 . The process of claim 12 , wherein:
heating the color separations comprises heating the color separations to 90° C.-110° C.; and
heating the molten film comprises heating the molten film to 120° C.-160° C.