WO 2015/036906 A1
Digital printing system
Landa Corporation Ltd.
In March/April 2015 another batch of patents covering the new technology being developed by Landa Digital were published. With a filing date of just 4 months after the first batch the changes are small, but still possibly significant. Here we review one concerning the intermediate transfer belt.
The Landa process is designed to produce high quality images on any existing commercial print papers using aqueous inks. To do this, images are formed on an intermediate transfer belt, dried and then transferred to the final substrate. The belt has a silicone rubber surface to give excellent release properties of the image to the final substrate. However that also means it is non-wetting to the inks which if nothing is done would bead and coalesce on the belt surface leading to very poor image quality. To solve this the belt is coated with a conditioning fluid just prior to the imaging station. The conditioning fluid freezes the drops in the flat round ‘impact’ form long enough for sufficient water to be removed, hence increasing the drop viscosity and immobilising it on the belt.
The figure shows a section through the imaging and transfer systems. Belt 102 passes through the cleaning and conditioning station 120 where any residual ink is removed and the conditioning fluid is applied ready for the next cycle. The belt then passes under printheads 106 which have hot air blowers 130 between each of them. These stabilise the drops by removing enough of the water to keep them in their ‘impact’ shape. The image then passes under drying station 108 where the drops are dried and rendered tacky ready for the transfer stage.
There are two transfer stations, and the substrate can be flipped in between them allowing duplex printing to take place. Before each transfer step dryers 210 can reheat the image, making it tacky again for transfer.
This patent application proposes that the belt be thinner than previously proposed. The thicker belt combined a compliant layer or blanket with the belt itself. The conformal layer is required to ensure that the image conforms to the surface structure of the substrate. Unfortunately the belt has been found to wear out despite the blanket having a greater working life.
The thin belt is paired with a compression layer on the pressure cylinders 110a and 110a’. The thin belt still has a conformal layer, between 100-400 microns, with the cylinder conformal layer much thicker at 2.5 mm. Using a thinner belt has several other advantages apart from increased life. There is a large reduction in mass and therefore the energy required to move it. The thermal inertia is also much lower, meaning that the time and energy required to heat it and cool it is reduced. Even so it seems that residual heat can build up in the belt, so the conditioning unit 120 can also be used to cool the belt.