EXPANDING APPLICATIONS LATITUDE WITH THERMAL INKJET

Non-impact printing technologies are the most suitable for a variety of industry applications.
The lack of contact between the print actuator and the support represents a significant advantage, forexample, in case of printing on moving objects, as occurs during the coding and marking of packaged
products in serialisation lines.
Developments in Microfluidics as well as ink formulations targeted to meet specific needs have enabled
the application of this technology on a wide variety of substrates, even and especially on non-porous
materials, ensuring both the printing quality and the level of resistance required by the performancestandards.
This synergy, in many cases, avoids any further application of a protective, transparent coating layer onto
the printed surface. Therefore, it is possible to produce simpler and less expensive printing systems,
suitable for non-porous media, while maintaining high-level performances.
With respect to the piezo inkjet print heads, which are largely used for non-impact industrial printing, thethermal inkjet devices (also named “bubble jet”) represents a lower total cost of ownership for certain
industrial and specialty applications, requiring easy user maintenance and a compact size of the hardware
device without compromising the highest standards in quality and reliability.
The interaction between the ink and print head, which is a critical factor in the thermal inkjet, has been
constantly optimised over time and together with the enhancement of ink formulations, more and morereliable materials have been developed. This constant improvement allowed the new inks to better match
both the functional behaviour and the printing performance of the device.
Unquestionably, the combination “thermal inkjet print head + ink” can be considered a rugged andreliable printing device nowadays as the thermal technology is able to replace the piezo technology in agreat number of implementations with excellent results.
In fact, where allowed by the application, the replacement of piezo actuators with thermal inkjet print
heads is already being broadly accomplished in the industrial installations. Such replacement is driven by
the need of cost reduction and sustained by the high quality and reliability standards, already wellestablished, making thermal inkjet a sound and cost-effective solution for the industrial printing businessas well.

THERMAL INKJET TECHNOLOGY AT SICPA
Product development at SICPA takes advantage of the combined efforts of two major R&D expertise:••

Print head design and development
Ink study and formulation

The synergic work between the two departments results in thesolid optimisation of the printing device: the ink, whose
formulation complies with the requests of specific applications, isejected by a print head, that is designed and intended to exploit
and enhance the ink performances. In the print head design, many
parameters play a role, such as:• Ink boiling characteristics and rheology• Required drop volume• Printing resolution• Maximum ejection repetition rate
which are among the most significant ones.
Through the print head design, the functional parameters aredefined. To go further into detail, the shape and size of both thefluidic circuit and the resistors are laid down and the energy
variables, such as current peak value and pulse duration, aredecided. Moreover, the operational temperature of the print
actuator is defined by design and effectively controlled through asuitable circuitry, according to the working conditions.

Thermal Inkjet printhead

By means of the numeric simulation, it is possible to follow the vapor bubble evolution in all its phases:
generation, expansion accompanied by ink ejection from the nozzle, collapse and finally, ink refilling of
the ejection chamber. Therefore, the working parameters of the print head can be assessed andoptimised with respect to the ink characteristics, the latter being in turn, dictated by the actualapplication.

Bubble evolution in time
Simulation of bubble volume (blue) and pressure(red)Generation - Expansion - Collapse

Nozzle refilling
Simulation of the meniscus movement from bubble collapse
to stabilisation. Damped oscillations are visible at the end of
the refilling time interval

Such an integration between ink and print head in view of the application allows the user to achieve highlevel performances, which are not accessible utilising mass market cartridges filled with non-original inks:
they are invariably bound to fail to meet quality standards, due to their unoptimised functioning. As aresult, moving towards an integrated printing system, such as that offered by SICPA, represents a real
breakthrough in industrial activity.

THERMAL INKJET PRINT HEADS PORTFOLIOThe Thermal Inkjet print heads, designed and developed by SICPA, may be divided into two macrogroups, having different cartridge sizes:••

Monochrome print head (swath length 1”)
Trichrome print head (swath length 2/3”)

The printing resolution, expressed in dots-per inch or dpi, and the dot size depends on both the layout
and the nozzle diameter as well as on the print head driving mode. Thus, the horizontal and verticalresolution can be effectively managed, according to the drop volume, the ink type and the medium
characteristics.

At present, what SICPA offers consists of a portfolio of well-established products; however, it should bepointed out that the modular architecture of the printing actuator allows the designers to customiseboth the ejector layout and the microfluidic circuit, without having to completely redesign the device’s
underlying electronics. Such flexibility makes it possible to broaden on demand and provided there is abusiness justification, the area of use. Hence, the requirements of a specific scope can also be satisfied
by a targeted print head.
The monochrome print head TYCHE has a swath length over 1” and a printing resolution up to 600x600
dpi, even though certain applications can take advantage of a printing mode performed at a lowerresolution.
The portfolio will be expanded with a TYCHE print head with high volume drops (about 30 picolitres)
and a printing resolution up to 300x300 dpi.
TYCHE
Water Based
25W
22W (UV)
Solvent
Based
18S
30S

Drop Volume[pl]2222Max Freq.
[kHz]
188

Drop Volume[pl]
12Max Freq.
Print Speed @300 dpi [m/min]
[kHz]
735
Under development

Print Speed @300 dpi [m/min]
9040

The trichrome print head CROMA has instead a swath length of 2/3” and a printing resolution up to1200x600 dpi; here too it may be convenient to reduce the actual printing resolution for certain
applications. CROMA is available in two versions with solvent ink and one version with water ink.

CROMA

10SW

Drop Volume[pl]10

Max Freq.
[kHz]
7Solvent
Based
10S
17S

Drop Volume
[pl]
612

Max Freq.
[kHz]
125

Water Based

Print Speed @300 dpi [m/min]
35
Print Speed @300 dpi [m/min]
60
25THE ADDED VALUE PROVIDED BY THE INKS
The inks for the bubble jet print heads that have been developed by SICPA to date, can be classified intwo groups:
Water-based inks
Water is the main vehicle in these formulations, which may also contain dyes and/or pigments. They
have been developed for printing on both porous and semi-porous media; water inks are widely used
for printing onto secondary and tertiary packages in the pharmaceuticals industry.
Solvent-based inks
The vehicle for dyestuffs of pigments is formed in this case by mixtures of various solvents, that aresuitably selected and put in the right proportion, in order to meet at best both the functionality and theadhesion strength on the substrate. Solvent inks have been developed for printing onto non-porous
plastic media (PVC, PET, PE, PC, etc.) and they found successful to use for the badge printing, often
adopted as identification cards by companies or as membership cards by stores.

INNOVATION NEVER STOPS: WATER BASED UV CURABLE INKS FOR THERMAL INKJET

The possibility to provide suitable solutions for covering a broad range of industrial applications, thatwater inks could not access for a long time, has raised a great interest right away. Among them, printing
on plastic and metal surfaces, coding & marking on pharmaceutical packages are the most attractive.
Hence, SICPA initiated a project to study and develop a family of water-based inks, which can be cured
using suitable UV LED lamps.
It is well known that the most outstanding elements, which can hinder the adoption of the traditional
water inks with non-porous media, turn out to be:•••Long drying time
Low adhesion strength to substrate and, in turn, short printout durability
Poor resistance to water and solvent exposure

Introducing the UV curing method and implementing it with water-based formulations lead to address all
the critical characteristics of the traditional inks, providing:•••Drying time consistent with the application requirements, i.e. lesser than 3 seconds
High adhesion to plastic and metal surfaces, demonstrated by the abrasion resistance values: up
to 5 times as high as that of the solvent inks, taken as a benchmark
Strong resistance to contact, immersion and rubbing with water and common solvents

It must be emphasised that the use of water-based UV inks within the industrial printing activities leads
to a dramatical decrease in the presence of organic volatile compounds (VOC) in the production lines,
with obvious advantages in terms of Health and Safety for operators and environment.
Some examples of printouts obtained with SICPA water-based UV curable inks are illustrated below:

Figure 1 - Alphanumeric printing on Stainless Steel

Figure 2 - QR Code printing on PET

Figure 3 - Data Matrix printing on Aluminium

Many other interesting aspects could be described in more detail, but this short review can alreadydescribe the capabilities of the digital printing solutions provided by SICPA Thermal Inkjet technologies.
For more information, please contact:
Roberta Sirio
B2B Sales Director, SICPA SA
Roberta.Sirio@sicpa.com
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