This document proposes a method for continuous printing with white ink by activating piezoelectric elements in the printhead at low power levels during idle periods. This "tickling" of the piezo elements steers the white ink in the printhead channels to prevent sedimentation and drying out of the heavy white pigment particles. Experimental results showed the printheads could maintain print quality for over 3 hours with this approach compared to failing after just 10 minutes without it. The method has been implemented on over 20 printers without issues reported by customers.

1. 1
A METHOD AND APPARATUS FOR PRINTING WITH WHITE INK
Semion Gengrinovich, Ran Vilk, Dennis Indorsky
Inkjet & Graphics Businesses, Scitex Devision, R&D HISS group
semion.gengrinovich@hp.com
Abstract
Key Innovation: Enables uninterrupted printing with white ink. The implementation of the method does not require
additional parts or material. Does not change established ink delivery patterns and systems
A method of printing with white ink by a piezo ceramic inkjet printhead, where the ink ejecting piezo ceramic elements are
activated at a certain power level at idle from printing periods to continuously steer the white ink in the printhead channel s.
The ink steering in the printhead channels prevents white pigment sedimentation and drying out on the nozzle plate and
around the nozzles. The ink steering takes place at idle of printing periods and in course of printhead accelera tion and
deceleration movements.
Problem statement
The printing is typically done by depositing colored ink on white substrates. Accordingly, all inks and color
control methods have been developed for use on white substrates. Recently, however, there is an increase in use
of clear or transparent and colored substrates. Faithful color reproduction on such substrates is complicate. In
order to alleviate influence of substrate color a white ink is used to provide an opaque background on a color or
transparent substrate. The specific weight of stable white pigment particles used in white ink formulation such as
TiO is three to four time larger than the specific weight of other color pigments. Because of this, the white
pigment particles tend to precipitate rapidly in the white ink. The precipitated particles form sediments that
introduce disturbances in printhead operation. The disturbances may be such that an irreversible damage will be
induced to the printhead. As it shown on Fig. 1 after 10 minutes of idle time the print heads can not print, this is
lead to ink waste during maintenance process and in most cases the ink waste can reach foe 1.5 – 2 liters of ink
for 104 print heads.
Fig.1
Signatures of PH’s with white ink immediately after maintenance a) and after 10 minutes of idle.
a) After maintenance
signature
b) After 10 minutes w/o
printing

2. 2
Our solution
The current solution suggests a method of maintaining operation of a printhead printing with ink containing heavy
pigment particles such piezoelectric actuators (see Fig. 2 Piezo element) are activated (tickled) almost on a
permanent basis. When printhead is not ejecting image forming ink drops and is idle, piezoelectric actuators are
activated may be activated at about the same operating voltage and frequency, but for a shorter pulse duration
Fig.2
Drawing of several nozzles in the print head.
time, for example, 2 to 4 microsecond. Such short drive pulse time does not cause ink drop ejection. Alternatively,
a third or a quarter of ink ejecting voltage ( 8-10V) at a lower frequency of about 2KHz to 4KHz and pulse length
of 2 to 4 microsecond could be applied to the printhead. Feeding the printhead at idle of printing periods by such
short pulses and low ink ejecting voltage does not cause ink droplets ejection, but is sufficient to case ink
movement in each respective ink channels (see Fig. 2). The movement of ink continuously steers the ink, but the
steering is not sufficient to cause ink drops ejection. Continuous ink steering prevents pigment precipitation and
sedimentation formation in channels and orifices nozzle as well as ink drying out on the nozzle plate and around
the nozzles. Continuous ink steering may be enhanced by ink purging procedures performed at idle of printing
periods.
Evidencethe solution works
We use tickle approach on the one of R&D machine with white ink. The non jetting mode was applied each 5
minutes for 1 minute. As it seen from Fig. 3 the white ink inside the print heads “stay fresh” for 3 hours.
1 2 3

3. 3
Fig. 3
1) Signature after maintenance 2) Signature after 1.5 hours with applying jetting mode 3) Signature after 3
hours with applying jetting mode.
The white ink kit installed on more than 20 machines on basis of FB7600 (Tamar), the ink waste of white ink
based on custumers data same as regular colors.
The link from DRUPA presentation of white ink: http://www.youtube.com/watch?v=8sltUqYS4hM
Competitive approaches
From our best knowledge the competitive approaches mostly based on some circulated ink delivery system and
more maintenance in terms of ink waste.
Currentstatus
Currently there are more than 20 white kits was sold and there is no complains from custumers, in general very
positive feedbacks.
Next steps
Currently there is a plans to create white option for FB10000 (Geffen platform) the non jetting mode will be part
of the maintenance.
References