Charge electrode assembly for ink jet printer

A charge electrode assembly useful in an ink jet printer comprises a nonconductive supporting structure in which a multiplicity of grooves are formed. Each groove has a conductive layer of a corrosion-resistant noble metal, preferably platinum or rhodium, thereby forming an electrode. An electric power supply is coupled to the electrodes and energizes selected ones of the electrodes when propelled ink droplets traverse the electrode area.

BACKGROUND OF THE INVENTION 
Some presently known ink jet printers employ a multiplicity of charge 
electrodes for controlling or modulating the stream of ink that is 
directed from an ink source to a record medium. An example of this type of 
printer is described in U.S. Pat. No. 3,373,437 entitled "Fluid Droplet 
Recorder With A Plurality of Jets", issued Mar. 12, 1968. One significant 
problem that has been encountered in arrangements of this type is the 
corrosion of the electrode material caused by anodic and cathodic 
dissolution. 
Another problem that is experienced is that a charge electrode which has an 
adhesion layer of transition metal under the functional coating tends to 
fail when used under cathodic current conditions because hydrogen is 
evolved, causing spalling and delamination of the coating. This requires 
undue maintenance and replacement with resultant increased cost and down 
time. 
It would be desirable to have a charge electrode assembly that would not be 
subject to corrosion or deterioration when used in an ink jet printer. 
SUMMARY OF THE INVENTION 
An object of this invention is to provide a novel and improved charge 
electrode assembly that will realize increased longevity and reliability 
when used in an ink jet printer. 
Another object of this invention is to provide a charge electrode that may 
be exposed to both anodic and cathodic current flow without dissolution, 
spalling or delamination. 
According to this invention, a charge electrode assembly for use in an ink 
jet apparatus is formed with grooves in a nonconductive support or 
housing. The surfaces of the grooves are coated with a conductive layer of 
a noble material, such as platinum or rhodium, to form discrete uniformly 
spaced charge electrodes. A direct current (DC) power supply is connected 
to the charge electrodes for selectively applying an electric potential to 
the electrodes as ink droplets traverse the electrode areas. The charge 
electrodes that employ a single material of a corrosion-resistant noble 
metal as the conductive element have been found to be resistant to 
degradation by the continuous impingement of highly pressurized ink jet 
streams or electrochemical attack and are able to maintain their 
conductivity without deleterious effects.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
With reference to FIG. 1, an ink jet printer comprises a nozzle plate 10 
having a multiplicity of nozzle elements 12 through which a pressurized 
electrically conductive jet of ink is propelled. The ink jet is vibrated, 
by piezoelectric means for example, so that each continuous jet of ink 
that is passed through each nozzle element is separated into a series of 
discrete droplets 14 which are uniform in dimension and spacing. 
A plurality of charge electrodes 16 formed on a charge plate 18 are 
interposed in the paths of the streams of the conductive ink droplets. In 
operation, a potential is selectively applied from a controlled power 
supply 20 to the charge electrodes 16, so that the ink droplets in the 
electrical field emanated by the charge electrodes will be capacitively 
charged or not charged, according to the potential that is applied to the 
electrodes at the instant that a droplet passes through the area of the 
electrode. 
The charged or uncharged droplets continue in their paths into an electric 
field generated by a deflection plate 22, which is connected preferably 
between a reference potential, such as ground, and a relatively high 
positive voltage source (not shown). The electric field established by the 
deflection plate 22 causes a slight deflection of those ink droplets that 
have a positive charge, so that these charged droplets will be deflected 
from the direction of travel and thus away from a target record medium 24. 
These deflected droplets are effectively removed from the stream of ink, 
and are gathered in a gutter 26, which may be formed with the deflection 
plate 22. In this way, the unused ink may be recaptured and recycled for 
use. 
The uncharged droplets which have not been deflected continue in their path 
and impinge upon the record medium or paper 24. Relative movement between 
the impacting droplets and the paper results in the registration of 
intelligent data which will form the desired record. 
In accordance with this invention as depicted in FIGS. 2A and 2B, the 
charge electrodes 16 are formed as uniformly spaced grooves 11 in the 
charge plate 18, which may be made from a nonconductive ceramic, by way of 
example. Within each groove, 11, a conductive layer 28 of a noble metal, 
such as platinum or rhodium is deposited. The conductive layer 28 may be 
deposited by sputtering techniques and may be about 1000A thick, for 
example. Each groove 11 may be 0.3mm wide, 1.5mm long, and 0.500mm deep. 
The charge electrode formed with the noble metal layer 28 is connected to 
a conductive strip 30 formed on the nonconductive ceramic housing 32 of 
the charge plate structure 18. A potential of predetermined magnitude that 
is provided by the controlled power supply 20 is passed through the 
conductive lead 30 to selected ones of the charge electrodes 16. An 
example of a charge electrode structure employing conductive elements is 
disclosed in U.S. Pat. No. 3,975,741, entitled "Charge Electrode for Ink 
Jet", issued Aug. 17, 1976. 
It has been found that the use of a passive noble metal, preferably 
platinum or rhodium, as the conductive layer of a charge electrode through 
which a stream of ink droplets is repeatedly passed, has enhanced the life 
and performance of the charge electrode. 
It should be understood that although platinum and rhodium have been 
designated as the preferred noble metals for use in the charge electrode 
assembly of a multiple ink jet printer, the invention is not limited to 
only these two metals, but contemplates the use of other noble metals of 
the platinum family. Also, it should be noted that the scope of this 
invention is not limited to the specific configuration and dimensions set 
forth in the description of the preferred embodiment, but may be applied 
to ink jet printers which employ one or more charge electrodes subjected 
to impinging ink droplets.