Single phase fluid gas extractor for electrophoretic purifier systems

An electrophoretic purifying system employing a gas/bubble filter is described, with the gas/bubble filter disposed in the path of a single phase liquid flow moving toward an electrophoretic purifier. The gas/bubble filter prevents bubbles, having a predetermined diameter, from entering the electrophoretic purifier. A rotating drum electrophoretic purifier is employed in which a rotating drum is in close proximity to a repelling electrode, defining a gap therebetween. The repelling electrode may be shaped as a cylindrical trough which houses an arcuate portion of the drum. Alternatively, the interior surface of the cylindrical trough may comprise of a repelling electrode. The gap is in fluid communication with a fluid outlet of a supply tank containing liquid having contaminants. The gas/bubble filter is disposed proximate to the fluid outlet, and the liquid flows therethrough to be purified. The gas/bubble filter includes a plurality of apertures, with each of the plurality of apertures being of appropriate size to block gas bubbles having a diameter within a predetermined range. In this manner, the liquid having contaminants is introduced into the gap and is substantially free of said gas bubbles. This prevents arcing which substantially improves the filtering efficiency of the electrophoretic purifier by maintaining a constant potential across the gap.

TECHNICAL FIELD 
The present invention relates to systems and methods for purifying liquids, 
and more particularly to the purification of liquid toners used in 
electrostatic printing. 
BACKGROUND ART 
Disposal of spent toners has long been a major problem for users of 
electrostatic plotters, printers and copiers. Environmental awareness, 
disposal costs, and strict governmental regulations relating to chemical 
handling and disposal have threatened the present manner of use of liquid 
toners. Purifying of toners presents a viable answer to these problems by 
reducing disposal amounts by allowing reuse of some of the toner. 
Presently, many prior attempts have been made to purify toners and other 
liquids. 
In U.S. Pat. No. 5,457,485 to Moriyama et al., an ink jet recording 
apparatus is disclosed in which a screen filter is disposed across a flow 
of ink. Operationally associated with the screen is a movable baffle. The 
movable baffle periodically moves into abutting relationship with the 
screen filter. In this manner, a substantial portion of the screen may be 
blocked, thereby creating a large pressure differential between the 
opposed sides of the screen, allowing bubbles to pass therethrough. This 
design allows the screen to sequentially block and transmit bubbles, 
depending upon flow direction. 
U.S. Pat. No. 5,426,459 to Kaplinsky discloses a thermal ink-jet pen 
cartridge having a check valve formed from a mesh having very small 
openings. The mesh openings are of sufficient size to prevent air bubbles 
from passing through under normal pressures. The check valve also serves 
to function as a particulate filter to prevent contamination of a 
printhead by particles from the ink reservoir. 
U.S. Pat. No. 5,346,000 to Schlitt discloses a heat pipe equipped with a 
bubble trap. The bubble trap includes a baffle that restricts the liquid 
flow in a liquid flow channel of the heat pipe, as well as a wire mesh. 
The wire mesh is positioned downstream from the baffle to entrap bubbles. 
U.S. Pat. Nos. 4,799,452; 4,895,103 and 4,923,581, all to G. F. Day, 
disclose methods for filtering liquid toner while eliminating the need for 
liquid toner disposal. In these methods, the toner itself is eliminated 
except for a transitory existence just at the moment of toning. 
Concentrated "ink" of each color is stored in a small tank and injected 
into and mixed with a continuous stream of clear dispersant. The resulting 
toner stream is passed through the toner applicator and then quickly 
decomposed back into concentrate and dispersant. This is achieved 
electrophoretically with a purifier, described in the above-referenced 
patents. The solid pigment particles are plated out on a rotating drum, 
then scraped off the drum and re-dispersed by vigorous mixing into the 
concentrate holding tank. To stop the toning process, the injection of the 
selected concentrate is simply terminated. 
It would seem that this recycling concept might provide a liquid toning 
technology free of disposal problems since a large volume of contaminated 
or spent toner would never exist. However, the basic cause of disposal is 
not eliminated. Eventually, the contents of the concentrate tanks would 
have to be discarded due to contamination, as would the fluid in the 
dispersant tank. This is because the contaminants are re-mixed with the 
dispersant along with the pigment particles and are, therefore, never 
removed from the system. The quantity of liquid to be thrown away would be 
smaller, but some disposal problems would remain. The dispersant would 
have to be discarded when the conductivity level became high enough to 
interfere with image toning. A much higher level of contamination could be 
tolerated in the color concentrate tanks because of the dilution upon 
injection into the dispersant stream, but eventually the concentrate would 
also need replacement. In addition, the recycling architecture is 
relatively complex. It requires precise metering and mixing of two fluid 
streams and high speed separation of the toner into its components as it 
flows out of its applicator. With the high flows which are characteristic 
of full-width toner applicators, the separation apparatus must be quite 
large and, therefore, costly. 
In order to electrophoretically separate a toner stream into its 
components, the fluid is passed between two closely spaced, parallel 
electrodes while a high voltage is imposed across the gap. All of the 
fluid must be exposed to the full electric field, and this means the flow 
must normally be confined to the gap region with some kind of fluid seals 
along the lateral edges of the separation zone. One of the electrodes 
should be moving so that the accumulating sludge can be scraped off and 
sent to the appropriate concentrate tank. The seals which confine the 
fluid flow within the gap present numerous technical difficulties. 
Commonly assigned U.S. Pat. No. 5,404,210 describes an electrophoretic 
filtering method and apparatus which continuously purifies small portions 
of liquid toner by using a rotating drum type to keep contamination below 
the level at which it will interfere with imaging. Spaced-apart from the 
rotating drum is a conductive electrode with the drum and electrode 
defining a gap therebetween. Rotating drum-type purifiers are effective at 
removing solid contaminants such as particles of color pigment, paper 
debris, and ions from the fluid dispersant. This requires a high voltage 
potential being present across the gap. The apparatus would benefit from a 
higher level of purification for each pass, which could be achieved by 
increasing the voltage potential across the gap. However, electrical 
breakdown keeps the applied voltage lower than would otherwise be desired. 
The reduced voltage potential necessitates a very large purifier for any 
given flow rate to assure substantial separation of the solids from the 
clear fluid. 
It is an object, therefore, of the present invention to provided an 
improved electrophoretic purifying system with an approach to reduce 
electrical breakdown between electrodes. 
It is another object to provide a purification system which is of reduced 
size and increased efficiency. 
BEST MODE FOR CARRYING OUT THE INVENTION 
The above objects have been achieved with a gas/bubble filter disposed in 
the path of a single phase liquid flow moving toward an electrophoretic 
purifier. By filtering bubbles, electrical breakdown is reduced. A 
rotating drum electrophoretic purifier is employed in which a rotating 
body is in close proximity to a repelling electrode, defining a gap 
therebetween. The repelling electrode may be shaped as a cylindrical 
trough which houses an arcuate portion of the body. Alternatively, the 
interior surface of the cylindrical trough may comprise of a repelling 
electrode. The gap is in fluid communication with a fluid outlet of a 
supply tank containing liquid having contaminants. The gas filter is 
disposed proximate to the fluid outlet and the liquid flows therethrough 
to be purified. The gas filter includes a plurality of apertures, with 
each of the plurality of apertures being of appropriate size to block gas 
bubbles having a diameter within a predetermined range. In this manner, 
the liquid having contaminants is introduced into the gap and is 
substantially free of gas bubbles having a diameter within the 
predetermined range. A voltage applied to the repelling electrode causes 
contaminants present in the liquid, i.e. mostly solids such as color 
pigment particles, in the case of liquid toner, to plate onto the surface 
of the rotating body. The body removes the contaminants, disposed thereon, 
from the gap, leaving semi-purified liquid which is substantially free 
from particulate contaminants. The contaminants may then be scraped off 
the body surface for disposal. The liquid is introduced continuously 
through an aperture positioned at the nadir of the electrode, centered at 
the bottom of the same. The semi-purified liquid bifurcates into two 
flows, each of which travels over the opposed edges of the electrode, 
spilling into a large funnel. 
In a first embodiment, the semi-purified liquid exiting the funnel is 
collected in a receptacle. The liquid collected in the receptacle is 
suitable for reuse, where it is stored until needed, for example, as clear 
fluid dispersant for color concentrate of a liquid toner. 
In a second embodiment, the semi-purified liquid passes through the funnel 
and into a second purifier formed from a container housing a porous 
contaminant-retentive material. The container includes an opening to allow 
semi-purified fluid to enter. Disposed opposite to the opening is a liquid 
outlet, allowing liquid to exit therefrom. The semi-purified liquid flows 
through the housing and passes through the porous material which contacts 
and retains the remaining contaminants, as by absorption, adsorption, or 
chemical binding. These contaminants may be ions generated by spontaneous 
ionization of molecules which were neutral during their transit across the 
gap of the drum purifier, or they may be neutral molecules. Liquid exiting 
the second purifier is substantially free of both particulate and 
non-particulate contaminants, defining purified liquid. The purified 
liquid exiting the second purifier is highly insulating and is suitable 
for reuse. The liquid is collected as discussed above with respect to the 
first embodiment. 
In a third embodiment, the second purifier includes a filter-type spiral 
having an elongated laminate preferably comprised of two electrically 
insulating, but porous, layers interleaved with two thin conductive 
layers. The laminate is spirally wound around a shaft and housed within a 
tightly-fitting cylinder having an opening for liquid inlet at one end and 
an opening for liquid outlet at the other end. After the liquid has passed 
through the drum purifier and solid contaminants have been removed, it 
flows axially through the cylindrical housing and passes through the axial 
length of the spiral laminate by flowing through the porous layers between 
the thin conductive layers. A voltage applied between the two conductive 
layers causes remaining contaminants, which are mostly ions generated by 
spontaneous ionization of molecules which were neutral during their 
transit through the gap of the drum separator, to be deposited on one or 
both of the conductive layers. The spiral laminate is of sufficient axial 
length and comprises numerous windings of its layers so that liquid 
passing through it is exposed to an electrical field for a long period of 
time and over a large area. The long time period allows the neutral, but 
ionizable, molecules to spontaneously ionize so that they can be 
effectively removed from the liquid. The liquid that exits the second 
separator is highly insulating and is suitable for reuse, for example as 
the clear fluid dispersant for color concentrate of a liquid toner.

BEST MODE FOR CARRYING OUT THE INVENTION 
With reference to FIG. 1, a drum purifier 10 is shown as including a 
rotating body 12 and an electrode 14 spaced-apart from body 12, defining a 
gap 16 therebetween. Body 12 is disposed to rotate about an axis 18 and is 
cylindrical in shape. Electrode 14 has a profile matching the profile of 
the body 12. Electrode 14 also includes a fluid inlet 20. A supply tank 22 
includes a fluid outlet 24 and contains liquid 26 having contaminants. 
Purifier 10 is in fluid communication with supply tank 22 vis-a-vis 
conduit 28 extending between fluid outlet 24 and fluid inlet 20. A scraper 
mechanism 30 is disposed proximate to body 12. Scraper mechanism 30 may 
comprise of a single blade disposed to be in continuous abutting 
relationship with the surface 32 of body 12. Alternatively, scraper 
mechanism 30 may comprise of a plurality of scraper blades each of which 
is selectively actuated to abut against surface 32, in a manner described 
in U.S. Pat. No. 4,799,452, which is incorporated by reference herein. Any 
blade included in mechanism 30 may be formed from thin steel. Preferably, 
a blade included in mechanism 30 is formed from a urethane compound and of 
a type widely used for scraping dry powder from drums in xerographic 
printers and copiers. 
Liquid 26 enters drum purifier 10 through fluid inlet 20 of electrode 14, 
filling gap 16. Electrode 14 is biased to repel particles within liquid 26 
which possess a like electric charge, such as toner particles. Debris 
particles from the imaging paper used in electrostatic printing and other 
contaminants tend to acquire a charge of the same polarity as the toner 
particles. Both toner and debris particles move through liquid 26 in gap 
16, adhering to surface 32 of body 12 as a slurry 34. As body 12 rotates, 
slurry 34 is removed from liquid 26 in gap 16 by scraper mechanism 30. 
To facilitate separation of slurry 34 from liquid 26, an air-knife 15 may 
be disposed adjacent to surface 32, providing a drier deposit to be 
present in tray 36, making the same easier to handle. To that end, 
air-knife 15 must be positioned relative to blade 30, so that drum 12 
passes slurry 34 by air-knife 15 before passing slurry 34 by blade 30. 
Air-knife 15 includes a body 17 having an air channel 19. The longitudinal 
axis 21 of air channel 19 extends orthogonally to surface 32. Air channel 
19 is in fluid communication with a supply of pressurized gas (not shown), 
i.e. air, via inlet 23 and typically extends across the entire width of 
drum 12. The gap width, from edge-to-edge of channel 19, is approximately 
0.005 inch. An envelope of gas exits the aperture of channel 19, proximate 
to surface 32, at approximately 0.5 pounds-per-square-inch and is focused 
thereon to separate liquid 29 present in slurry 34. The aperture is 
positioned approximately 0.015 inch away from surface 32. To prevent back 
pressure from developing in channel 19, the body 17, proximate to surface 
32, tapers upwardly away therefrom, forming an angled portion. In this 
fashion, air exiting channel 19 separates a substantial amount of liquid 
29 present in slurry 34, allowing it to return to gap 16 or flow into 
funnel 42. 
Referring also to FIG. 2, body 12 is disposed between spaced-apart side 
plates 46, which position the various components relative to each other. 
An axle 48, which defines axis 18, is connected to a gear motor, not 
shown, to rotate body 12. Body 12 is preferably 3.5 inches in diameter and 
3.5 inches in length, but the aforementioned dimensions may be varied for 
other applications. Repelling electrode 14 covers approximately 
120.degree. of the bottom of body 12, forming an arcuate trough with its 
end edges at the same height as its lateral edges. Alternatively, 
repelling electrode 14 may be housed within the interior surface of a 
trough or other means of containing liquid and keeping electrode 14 in 
close electrical communication with body 12. Gap 16 is approximately 0.015 
inch in width. The applied voltage is approximately 2200 volts 
corresponding to a field of about 147,000 volts per inch. Different 
combinations of gap width and voltage may be used, but this combination is 
practical from the standpoint of flow capability. Wider gaps require 
higher voltage and are more prone to electrical breakdown. Narrower gaps 
can restrict the liquid flow too much. 
Referring also to FIG. 3, generally, gap 16 should be in the range 0.010 to 
0.025 inch and the applied voltage in the range of 1000 to 4000 volts, but 
other combinations may be practical, depending on the size of body 12 and 
the characteristics of the liquid to be purified. It is preferred to 
maintain as high a voltage as possible in order to efficiently remove 
charged contaminants. It was discovered, however, that gas bubbles present 
in liquid 26 tend to break down electrically and produce an arc when 
exposed to the applied voltage in gap 16. The arc creates a momentary drop 
in voltage which reduces the purification efficiency, i.e., purification 
action is essentially halted during the momentary reduction in voltage. 
Although the applied voltage could be reduced to prevent arcing, such a 
reduction would decrease purification efficiency. To overcome problems 
with bubbles, a gas/bubble filter 50 is disposed in the path of liquid 26 
moving through fluid outlet 24. Although filter 50 may be disposed 
anywhere along the flow path preceding drum purifier 10, it is preferred 
that filter 50 be disposed proximate to fluid outlet 24. In this manner, a 
single phase flow moves across filter 50, and bubbles 52 present in liquid 
26, accumulating on filter 50, may easily move upward toward the top 54 of 
liquid 26. Upon reaching top 54 of liquid 26, a bubble may escape into the 
atmosphere, shown as 56. 
Referring also to FIG. 4, filter 50 includes a plurality of apertures 58, 
with each of the plurality of apertures 58 being of appropriate size to 
block bubbles 52 having a diameter greater than or equal to 0.0029 inch. 
To that end, filter 50 comprises of a nylon screen with the plurality of 
apertures 58 formed from a plurality of intersections 60 of thread 62 
having a diameter of 0.002 inch. This type of material is available from 
McMaster-Carr Supply Company. With filter 50, liquid 26 introduced into 
gap 16 is substantially free of bubbles 52 having a diameter greater than 
0.0029 inch, and no arcing is observed. To further reduce the chance of 
electrical break-down of liquid 26, opposed edges 38 may be formed so that 
gap 16 is approximately 0.060 inch in width, as shown in FIG. 2. 
Referring to FIGS. 1-4, in operation, each blade of mechanism 30 extends 
across the entire length of body 12's cylindrical surface. This allows 
mechanism 30 to clean surface 32 and prepare body 12 for further plating 
of contaminants on a subsequent pass across gap 16. After being removed 
from surface 32, slurry 34 is collected in a waste tray 36, disposed at 
one end of mechanism 30. Liquid remaining in gap 16 eventually spills over 
opposed edges 38 of electrode 14 as more liquid flows through conduit 28. 
Liquid spilling over opposed edges 38 is substantially free of particulate 
contaminants, forming a semi-purified liquid 40. The semi-purified liquid 
40 is collected by a catch funnel 42 which is positioned below electrode 
14. In this fashion, gravity moves semi-purified fluid 40 into funnel 42. 
Funnel 42 preferably has sloped sides and a central opening 44 which 
allows for drainage of the partially-purified liquid 40 from drum purifier 
10. After exiting central opening 44, semi-purified liquid may be 
collected in a receptacle, not shown, where it is stored until needed 
again for use. The flow rate of liquid 40 is equal to the flow rate of 
liquid 26 through fluid inlet 20 and may be adjusted so that the 
contaminants are plated out before the fluid reaches the lateral edges of 
body 12. Typically, a pump 11 is in fluid communication with conduit 28 to 
move liquid 26 therethrough at approximately 0.35 gallons/minute. However, 
liquid 26 may be fed through conduit 28 via gravity. To achieve gravity 
feed, supply tank 22 would be at approximately the same level as drum 
purifier 10, or higher. The top of opposed edges 38 are positioned 
somewhat above fluid outlet 24 so that supply tank 22 never empties 
completely into gap 16. This insures that gap 16 remains filled, up to the 
opposed edges 38, with liquid 26 to prevent air from ingressing therein, 
which also prevents arcing. 
In the case of liquid toner, isopar G, a volatile petroleum product 
available from Exxon Corp., often serves as the clear fluid dispersant for 
color concentrate particles. The drum purifier operates at a rotational 
rate of approximately 7 rpm, which is sufficient time to enable liquid 26, 
removed from gap 16 by surface 32, to return to gap 16, leaving viscous 
slurry 34 on surface 32. Slurry 34 moves slowly toward scraper mechanism 
30 at a rate to allow any liquid contained therein to partially evaporate. 
Thus, the contaminants removed by drum purifier 10 dry into chunks which 
easily break off and fall into waste tray 36. Waste tray 36 is removable 
for periodic emptying. 
FIGS. 5 shows an alternate embodiment of the system in which a second 
purifier 66 is disposed to receive semi-purified fluid 40 exiting central 
opening 44. Second purifier 66 is configured to remove molecules that are 
neutral or that have ionized since leaving drum purifier 10. Second 
purifier 66 typically includes a housing 68 containing a packed bed of a 
porous material 70 that is particulate or granular, and through which 
liquid 40 can pass. 
Porous material 70 is preferably activated charcoal, available from 
American Norit Corp., which is economical and effective at removing a 
large number of chemical species from liquids. Other appropriate porous 
materials include diatomaceous earth and zeolite, which is available from 
Union Carbide Co. Similar materials which have a large surface area and 
which remove contaminants from a liquid via absorption, adsorption, or 
chemical binding may be substituted. "Contaminant-retentive" as used here 
signifies retention via absorption, adsorption, or chemical binding. The 
grains that make up the porous material 316 are preferably in the range of 
0.0004 to 0.04 inch. Smaller grains tend to impede liquid flow through the 
purifier. Larger grains do not provide good exposure of all portions of 
the liquid to the surfaces of the grains within porous material 70. 
Porous material 70 need not completely fill housing 68, but preferably 
completely fill a cross section of the same so that all liquid 40 flowing 
through second purifier 66 traverses porous material 70. On each end of 
housing 68, end caps 72 are disposed. Each end cap 72 includes opening for 
liquid inlet 71 and outlet 73. Preferably, housing 68 also includes 
screens 74, which are disposed proximate to each end cap 72 to allow 
passage of liquid 40, while retaining porous material 70 within housing 
68. To that end, porous material 70 is typically wedged between screens 
74, with liquid emerging from outlet 73 defining highly purified liquid 
76. Purified liquid 76 is substantially free of both particulate and 
non-particulate contaminants and is collected by a receptacle, not shown, 
so that it may be reused, e.g. as fresh fluid dispersant. Color 
concentrate particles may be added to liquid 76 for the creation of liquid 
toner. 
For liquid toner purification, second purifier 66 is preferably 
approximately four inches in axial length and four inches in diameter. 
These dimensions and shapes may be adjusted as appropriate for the 
application. The porous material 70 also serves to counteract possible 
discoloration of the liquid due to oxidation, in the liquid toner 
application. Oxidation, if excessive, can affect the imaging properties of 
the liquid toner. Oxidation of liquid toner can also be inhibited by 
chemical anti-oxidants, as is well known in the liquid toner formulations 
art. 
Referring also to FIG. 6, in a third embodiment, second purifier 166 
includes a spiral laminate 180 contained within a cylindrical housing 168 
to remove molecules that have ionized since leaving drum separator 10. 
Spiral laminate 180 contains spirally-wound porous and conductive layers. 
Liquid enters spiral separator 166 through inlet 171 of an end cap 172 and 
passes through the porous layers of spiral laminate 180, exiting outlet 
173. Liquid is subject to an electric field between the conductive layers 
of spiral laminate 180. This electric field results from voltage 
application to leads 184, each of which is connected to one of the 
conductive layers. Any ionic contaminants within the liquid migrate to a 
conductive layer, according to their net electrical charge. Liquid 176 
emerging from second purifier end cap 166 is in a highly purified, 
insulating, stable form. It may then be reused, e.g. as fresh fluid 
dispersant to which color concentrate particles may be added, for the 
creation of liquid toner. 
Referring also to FIG. 7, spiral laminate 180 is made up of alternating 
layers of porous material 186, such as continuous-filament polypropylene 
paper, available from Kimberly-Clark, and electrically conductive material 
188, such as aluminum foil. Spiral laminate 180 is tightly wound around a 
supporting shaft 190 and then inserted into a close-fitting housing 192. 
The layers are attached to shaft 190 so that conductive layer 188 is 
first, with porous layer 186 wrapping around conductive layer 188. In this 
manner, conductive layer 188 occupies the innermost position in the 
finished spiral. As many alternating layers of laminate may be used, as 
desired. For convenience in winding, the leading edges of the respective 
layers may be taped, using insulating, self-adhering tape, to shaft 190 
and to each other. When the laminate is substantially wound, conductive 
layer 188 is extended around the spiral once more, providing an 
electrically conductive and relatively biased outer layer. This ensures 
that porous layers 186 are entirely sandwiched between conductive layers 
188 and that liquid traveling through the porous layers of spiral laminate 
180 will be subject to the electrical field throughout its traverse. 
Porous layers 186 are adjusted slightly in width and length as necessary 
to prevent conductive layers 188 from contacting each other directly and 
causing an electrical short. 
For liquid toner purification, spiral laminate 180 is preferably 
approximately four inches in axial length, four inches in diameter, and 
wrapped around a shaft that is an aluminum rod, three-eighths of an inch 
in diameter. The conductive layers 188 are generally 0.001 inch thick and 
the porous layers 186 are 0.01 to 0.02 inch thick. The layers are of 
sufficient length to allow for approximately forty turns around shaft 190, 
in the preferred embodiment. All of these dimensions may be adjusted as 
appropriate for the application. Electrical leads, such as thin wires 184, 
are placed in contact with conductive layers 188 to bias the conductive 
layers relative to each other. Electrical leads 184 may extend out of 
second purifier 166 through an end cap 172, as shown, with inlet 171 
sealed to prevent liquid leakage. As liquid passes through spiral laminate 
180 it is subject to approximately 600 volts applied between electrical 
leads 184. Charged particles are attracted to one of the conductive layers 
188, depending on their electrical charge polarity. The remaining liquid 
continues to pass through second purifier 166 and emerges in a 
substantially ionic-contaminant-free condition. Second purifier 166 may 
optionally contain a layer of activated charcoal 194 proximate to outlet 
173 where liquid emerges therefrom. Charcoal layer 194 counteracts 
possible discoloration of the liquid due to oxidation, as discussed above. 
Screens, not shown, may be disposed within cylindrical housing 182 to 
separate charcoal layer 194 from spiral laminate 180, or a cloth bag 
containing activated charcoal may be used. 
Another possible embodiment of the present invention includes the use 
filter 150 to block bubbles, as discussed above with respect to FIGS. 1-5. 
Filter 150 may be disposed proximate to second purifier 166 just before 
liquid exiting drum purifier 10 enters an inlet, as shown in FIG. 5. 
Additionally, laminate 180 may be altered to some configuration other than 
a spiral. A spiral winding was implemented simply to confine the various 
layers efficiently to a small space and because such a configuration is 
easy to produce. 
The purification systems discussed with respect to FIGS. 5-7 are of 
particular utility in situations where the liquid to be purified contains 
charged particles, as well as neutral molecules that either ionize slowly 
or not at all. Use of drum purifier 10 to remove color pigment particles 
and other charged particles, followed by a second purifier to remove 
further neutral and ionic contaminants, results in a clear, highly 
purified liquid that is virtually free of charged particles and other 
contaminants and which remains highly insulating in storage. In the liquid 
toner example, the ionization kinetics of the contaminant molecules are 
relatively slow. Drum purifier 10 removes existing ionic contaminants from 
the liquid, but the ionized fraction of contaminant molecules is small. To 
remove substantially all of the contaminants, purification via drum 
purifier 10 is followed by the second purifier to remove neutral 
molecules, as well as some previously neutral molecules that have become 
ionized are thereby removed. 
The purifier system and method of the present invention may be used to 
purify for reuse liquid toners which have been removed from electrostatic 
printing systems. This may be done by using the purifiers discussed above 
in a location removed from the electrostatic printing system. The purified 
dispersant may then be used for mixing new toners, for return to a toner 
manufacturer for credit towards a new toner purchase, or to enhance the 
purity of newly purchased dispersant. Another manner of carrying out the 
present invention is by incorporating the purification system into a 
continuous electrostatic printing and toner purification system. 
FIG. 8 shows a continuous electrostatic printing and toner purification 
system. Large arrows indicate liquid flow and small arrows indicate air 
flow. The lines that contain both large and small arrows carry both liquid 
and air. The colors black, cyan, magenta, and yellow are typically used in 
a four-color printing system and are shown in toner receptacles 201-204, 
respectively. The color toners are continually pumped out of their toner 
receptacles and circulated up to the region of input selector manifold 
205. When a particular color is to be used, the valve 206-209 
corresponding to the color is opened and the color toner enters input 
selector manifold 205. From there, it is directed to toning applicator 210 
which contacts the paper or other printing surface and which may extend 
the full width of the web upon which the printing will occur. Receptacle 
211 contains wash fluid, i.e. the same clear fluid dispersant, such as 
isopar G, that is used to disperse color pigment particles to make the 
color toners contained in toner receptacles 201-204. The wash fluid is 
circulated and in connection with input selector manifold 205 in the same 
manner as the color toners. 
After a color toner has been applied to paper via toning applicator 210, 
the liquid remaining within toning applicator 210 is substantially removed 
by an air purge loop having its source at blower 212. The color toner is 
drained back into the appropriate toner receptacle through the operation 
of the air purge and the appropriate valve 213-216. Approximately 0.17 
U.S. fluid ounce of color toner is purposely left behind in toning 
applicator 210. Then toning applicator 210 is washed via a pass of 
approximately 10.5 U.S. fluid ounces of wash fluid which carries away the 
0.17 U.S. fluid ounce of color toner left behind in toning applicator 210 
from the previous color pass. The dirty wash fluid then drains into 
holding supply tank 22 before it enters into the purification system of 
the present invention. The next color toning pass is started by the 
opening of one of the valves 206-209, flow of the selected color into 
input selector manifold 205, and input of the color toner into toning 
applicator 210, as with the previous color pass. Wash fluid passes occur 
between color passes so that there is no cross-contamination of the 
different color toners. Generally, four-color printing occurs via separate 
color passes in a dark to light sequence, so the typical order of liquid 
usage is as follows: black toner, wash, cyan toner, wash, magenta toner, 
wash, yellow toner, wash. 
The air purge loop within this system is optional, as drainage of toning 
applicator 210 may be effected by other means, such as gravity flow. The 
use of an air purge loop through the various lines is preferable, however, 
as it allows for rapid, controlled removal of color toner from toning 
applicator 210. The air purge loop includes blower 212, pressure manifold 
217, and valves 218-220 for purging of various drain and supply lines. An 
air jet cleaner is described in commonly assigned U.S. Pat. No. 5,231,455, 
which is incorporated by reference herein. A mixture of air and dirty wash 
fluid enters supply tank 22. Liquid 26 having contaminants may be 
gravitationally drained from supply tank 22 and enters to enter drum 
purifier 10. Alternatively, liquid may be drained from supply tank 22 by 
pressurization or vacuum. The air in supply tank 22 is removed via an 
outlet at or near the top of the same, and reenters the air lines and 
eventually the inlet of blower 212. An internal baffle may help reduce 
splatter within supply tank 22. In the same manner, the mixture of air and 
color toner that drains into toner receptacles 201-204 is separated by 
gravity. Air is removed from each toner receptacle through an outlet at 
the upper portion of the toner receptacle and reenters the air lines. 
During a color pass, the toning process carries out some of the color 
pigment particles as visible image. The toner within the electrostatic 
printing system leaving toning applicator 210 is therefore somewhat 
diluted in terms of color pigment percentage. Therefore, color concentrate 
from concentrate bottles 221-224 may replenish the color toner in toner 
receptacles 201-204, as necessary. 
After dirty wash fluid has passed through supply tank 22, it first enters 
drum purifier 10 and then second purifier to undergo the purification 
process of the present invention. Purified wash fluid, which is clear, 
low-conductivity isopar in this example, emerges from the second purifier 
and reenters wash fluid receptacle 211 for reuse in the system. The clear 
dispersant in receptacle 211 is thereby kept in a high purity, highly 
insulating condition. Mixing of a portion of the wash fluid into the 
toners therefore does not degrade the toners. 
The electrostatic printing system depicted in FIG. 8 incorporates a 
continuous purification system. Each color toner pass and subsequent air 
purge leave approximately 0.17 U.S. fluid ounce in toning applicator 210. 
The washing process carries this 0.17 U.S. fluid ounce of color toner and 
any other paper debris or chemical contaminants received from the contact 
of toning applicator 20 and the printing surface out of toning applicator 
210 and into the two purifiers. The clean wash fluid reenters wash fluid 
receptacle 211 and is reused for subsequent washing of toning applicator 
210. After washing and air purging of the wash fluid, there remains as 
much wash fluid in the applicator, 0.17 to 0.35 U.S. fluid ounce, as there 
was toner after toner purging. Normally, each liquid is purged into its 
respective holding receptacle. Each toner receptacle has a level sensor, 
however, and, if the contents of a toner receptacle drop below a 
pre-determined level, the wash fluid may be purged into that receptacle to 
control the liquid level. In this way the liquid level in each toner 
receptacle is automatically controlled. The user need only resupply clear 
liquid dispersant to the wash fluid receptacle. This is a neat and clean 
process because colored toners are not involved. As needed, fresh bottles 
of concentrate may be replaced by simply unscrewing the empty bottle and 
replacing it with a new one. These new concentrate bottles may have neck 
seals consisting of thin foil. The new bottle is raised towards a mounting 
supply tank causing a concentrate withdrawal needle to penetrate the foil. 
The clean plastic cap from the new bottle is used to seal the empty 
bottle. Thus the replacement of concentrate is also a clean, non-messy 
process. As the user never has to handle toners themselves, operation of 
the printer is a clean process and suitable for an "office" environment. 
The applicator and associated plumbing is self-cleaning since it is washed 
by the wash fluid. 
The amount of contaminants removed from a toner by the purification system 
during a color pass is proportional to the amount of toner left in the 
toning applicator after purging with air. By adjusting the time duration 
of air purging, this amount of residual toner can be controlled. It is 
believed that contact of the toner with the printing paper during a toning 
pass introduces a small amount of deleterious contaminants into the toner. 
Thus a fixed amount of contaminants is likely to be introduced per pass. 
On the other hand, the amount of contaminants removed per pass is 
proportional to the contaminant concentration. This means that the 
contaminant concentration will slowly build up until the amount removed 
per pass just balances the amount picked up per pass and the limit is 
approached asymptotically. By adjusting the air purging time, this 
steady-state contaminant level may be held to any desirable level. With 
very brief air purging, more toner is left behind to be intermixed with 
the wash fluid and removed from the system. This results in a lower 
steady-state contamination level. It also results in a larger amount of 
solid waste in the tray to be discarded, but the amount of waste is, at 
most, only a few grams per day. This is insignificant in comparison to the 
large amount of liquid waste produced in the prior art. The drum purifier 
lasts indefinitely and does not require replacement. The second purifier 
has long life depending on its size and composition, because most large 
particles have been removed before the liquid enters the second purifier. 
The continuous purification system described is similar to that disclosed 
in commonly assigned U.S. Pat. No. 5,404,210, which is incorporated by 
reference herein. 
A user of an electrostatic printing system containing the purification 
system of the present invention need only throw out solid contaminants 
collected in waste tray 36, replace color concentrate bottles 221-224 
because color pigment particles are used for the images printed and a 
small amount is lost through the purification system, and add wash fluid 
which is steadily lost to the printed paper and to some evaporation within 
the system. All of these tasks need only be performed on an occasional 
basis. In one week of operation of an electrostatic printer having the 
tandem purification system, at a rate of eighty large color prints per 
day, about two ounces of solid contaminants are collected and need to be 
discarded. The amount of waste and ease of removal of that waste represent 
a significant advancement over previous methods. The requirement of 
removing and disposing of large volumes of spent toner has been 
eliminated.