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Technology :
The term ink jet covers
the collection of printing techniques that operate according to the
principle that the ink droplets are jetted directly onto the
substrate. The basic part of an ink jet printer consists of the
print head and the ink. The print head contains many identical,
microscopic – small ink channels. Each channel produces thousands of
ink droplets per second. In order to get a satisfactory print
quality, a highly accurate reproduction of droplet formations is
essential. For realization of the ink droplets, in practice various
operating principles have been developed. A rough subdivision of
these principles yields the following two major categories:
continuous ink jet and drop – on – demand (DOD) ink jet.
The DOD type comes in two
types, thermal and piezo – electrical DOD ink jet.
An overview of non –
contact ink jet technologies:
1.Continuous
ink jet (CIJ)
CIJ uses a method where by the ink is jetted continuously from all
print head nozzles with every droplet being given an electrical
charge. This charge determines whether or not the droplet reaches
the substrate or is deflected back into the system to be recycled
and reused. Continuous ink jet is used principally for l very high
speed coding and marking and it requires sophisticated auto ink
viscosity control systems.
2.1. Piezo drop on demand binary ink jet
This printing process uses PZT material that deforms when an
electric field is applied to it. This deformation is harnessed in
order to eject the ink from the print head in a highly controlled
and repeatable manner. Each pixel on the substrate is either covered
with ink or not – a binary choice. It is seen in a range of
industrial printing applications, including coding and marking, as
it is a versatile technology able to print on a wide variety of
surfaces with virtually any type of ink.
In simplified overview, Metsa systems print head technology consist
of a series of ink chambers packed together into a print head,
divided by shared channel walls with an electrode attached to each.
When an electric current is put through the electrodes, the channel
walls deform to eject onto the substrate. The area of this
technology which has been particularly well patented by Xaar is its
unique use of shear mode printing.
This means that the deformation of the ink chambers that takes place
is in the manner of the movement of pack of cards when sheared to
one side-the height and of the chambers does not alter, they simply
just shift from one side to another and it is this movement that
ejects the ink. Shear mode is more efficient than the direct mode of
printing employed by other ink jet technologists as it's effect a
greater deformation in the ink is ejected in a highly controlled
manner in order to produce accurate quality printing.
2.2. Thermal DOD inkjet
Thermal inkjet (TIJ) heads are mass-produced for color ink jet
printers in home and office environments, often called the SOHO
(small office and home office) market. Subsequently such heads have
been built into machines for CAD, drafting, mapping, and wide-format
printers by some companies.
Thermal inkjet droplet formation
In thermal DOD print heads, a heating element receives a short
electrical charge that momentarily raises its surface temperature to
650-750° (350-400° C). The heat causes a thin layer of ink bordering
the heater to nucleate and vaporize, forming a bubble that expands
rapidly. The expanding collapses, simultaneously drawing more ink
into the channel from a reservoir.
2.3 Piezo DOD inkjet
There are many piezo DOD heads that are also manufactured for the
SOHO market, once again, the product performance and reliability are
very strong with these piezo heads, and they have been built into
several wide-format printers.
Piezo print heads typically last loner than thermal heads, although
fewer are made, and they are more ex-pensive to manufacture.
So at one extreme, we have the huge ink droplets produced by most
CIJ and piezo CIJ systems. At the other, we have the minute droplets
produced by photorealistic home and office inkjets based on thermal
DOD or piezo DOD heads. In between is the range of resolution
requirements and ink deposits needed for most wide-format
applications. Such application also requires direct printing onto
raw and uncoated substrates, rather than high-cost specialty media,
which implies a need for something beyond water-based ink-namely
solvent –based and UV-curable inks.
These facts therefore suggest that these needs can be met by only
one branch of the inkjet family: piezo DOD heads. Not all piezo
heads are created equal. Among the large portfolio of piezo head
manufactures and architectures, heads are available that are based
on water, solvent, or oil. Some are even designed for UV-curable,
hot-melt, or hybrid ink systems. Available piezo DOD systems include
those that can print fast and those that print less quickly.
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