Replenishing system

An apparatus for measuring concentrations of a first vapor pressure carrier fluid component and a second vapor, pressure carrier fluid component in a carrier fluid mixture, including a supply vessel for holding the carrier fluid mixture. A light source is provided for transmitting an infrared light source to the carrier fluid mixture. Detector is provided for detecting infrared light intensity transmitted through the carrier fluid mixture, and, in response thereto, determining infrared absorption of carbon hydrogen stretching frequencies of the carrier fluid mixture. And means are provided for calculating concentrations of the first carrier fluid component and the second carrier fluid component in the mixture based on the infrared absorption of carbon hydrogen stretching frequencies of the carrier fluid mixture. This method can also be extended to a mixture of more than two fluids. A means for maintaining a predetermined ratio of the carrier fluids.

FIELD OF THE INVENTION 
This invention relates generally to an electrophotographic printing 
machine, and, more particularly, concerns a method and apparatus for 
replenishing liquid developers having mixed carrier fluids. 
BACKGROUND OF THE INVENTION 
The use of liquid developers in electrophotographic printing machines is 
known. Liquid developers have many advantages, and often result in images 
of higher quality than images formed with dry toners. The toner particles 
can be made very small without resulting in problems often associated with 
small particle powder toners, such as machine dirt which can adversely 
affect reliability, potential health hazards, limited crushability, and 
restrictions against the use of coarsely textured papers. Development with 
liquid developers in full color imaging processes also has many 
advantages, such as a texturally attractive print because there is 
substantially no height build-up, whereas full color images developed with 
dry toners often exhibit height build-up of the image where color areas 
overlap. Further, full color prints made with liquid developers can be 
made to a uniformly glossy or a uniformly matte finish, whereas uniformity 
of finish is difficult to achieve with powder toners because of variations 
in the toner pile height, the need for thermal fusion, and the like. 
Ideally, such liquid developers should be replenishable in the particular 
equipment in which they are used. In general, high solids concentration 
toners are used for replenishment because relatively low concentrations 
(e.g., in the range of 10 to 15% by weight solids) result in greater 
liquid build-up in the equipment, which then must be removed and disposed 
of as hazardous waste. Thus, it is desirable to initially use a toner 
containing less liquid, and to maintain the working source located within 
the equipment, thereby minimizing the undesirable accumulation of carrier 
liquid in the equipment. In addition, it is highly desirable and 
economically attractive to have the liquid vehicle containing the toner 
particles to be recovered economically and without cross contamination of 
colorants. 
The application of liquid developer to the photoconductive surface clearly 
depletes the overall amount of liquid developer in the reservoir of an 
electrocopying or electroprinting machine of this type. In practice, the 
liquid reservoir is continuously replenished, as necessary, by addition of 
two liquids from two separate sources, the one providing carrier liquid 
and the other-a concentrated dispersion of toner particles in the carrier 
liquid. This is necessary in order to maintain in the carrier liquid in 
the reservoir a relatively constant concentration of toner particles, 
because the total amounts of carrier liquid and toner particles utilized 
per electrocopy vary as a function of the proportional area of the printed 
portions of the latent image on the photoconductive surface. An original 
having a large proportion of printed area will cause a greater depletion 
of toner particles in the liquid developer reservoir, as compared to an 
original with a small proportion of printed area. Thus, in accordance with 
the aforementioned practice, the rate of replenishment of carrier liquid 
is controlled by monitoring the overall amount or level of liquid 
developer in the reservoir, whereas the rate of replenishment of toner 
particles (in the form of a concentrated dispersion in carrier liquid) is 
controlled by monitoring the concentration of toner particles in the 
liquid developer in the reservoir. An optical float can combine both these 
functions, i.e. can be utilized to monitor both the overall amount of 
liquid developer in the reservoir and the toner particle concentration 
therein. The amount of toner particles utilized per electrocopy varies in 
proportion to the relative printed area of the image. Thus, a large number 
of so-called "white" copies (i.e. originals with small printed areas) will 
result in very small depletion of toner particles whereas the amount of 
carrier liquid depleted will be comparatively large. 
It has been found that it is highly desirable to employ carrier liquid 
compositions and, in particular, to liquid developers comprised of a 
mixture of high and low vapor pressure fluids, and wherein there is 
enabled with such developers excellent fixing characteristics especially 
when the developed image is transferred from an intermediate substrate to 
the final substrate, such as paper, reference for example U.S. Pat. No. 
5,276,492, the disclosure of which is totally incorporated herein by 
reference. U.S. application Ser. No. 08/461,829 entitled "LIQUID DEVELOPER 
COMPOSITIONS" the disclosure of which is totally incorporated herein by 
reference discloses developers and processes for achieving high fix 
wherein the developers contains a high vapor pressure fluid, such as an 
Isopar, like ISO L.RTM., and a low vapor pressure fluid, such as Norpar 
15, Superla NF5, and the like, and which low vapor pressure fluid is 
substantially odorless. The high vapor pressure fluid in embodiments is 
removed by heat once the developer is transferred to the intermediate 
substrate, and the low vapor pressure fluid remains with the developer 
when the developed image is transfixed, that is transferred, fixed and 
heated simultaneously, to a supporting substrate like paper. 
SUMMARY OF THE INVENTION 
In accordance with one aspect of the present invention, there is provided 
an apparatus for measuring concentrations of a first vapor pressure 
carrier fluid component and a second vapor pressure carrier fluid 
component in a carrier fluid mixture, including a supply vessel for 
holding the carrier fluid mixture. Means are provided for transmitting an 
infrared light source to the carrier fluid mixture. Means are provided for 
detecting infrared light intensity transmitted through the carrier fluid 
mixture, and, in response thereto, determining infrared absorption of 
carbon hydrogen stretching frequencies of the carrier fluid mixture. And 
means, responsive to said examining means, are provided for calculating 
concentrations of the first carrier fluid component and the second carrier 
fluid component in the mixture. 
In accordance with another aspect of the present invention, there is 
provided an electrophotographic printing machine for producing an image on 
a recording sheet, having means for recording a latent image and means for 
developing the latent image with liquid developer composed of a first 
vapor pressure carrier fluid component and a second vapor pressure carrier 
fluid component in a carrier fluid mixture, said developing means, 
including means for measuring concentrations of the first vapor pressure 
carrier fluid component and the second vapor pressure carrier fluid 
component in a carrier fluid mixture.

While the present invention will be described in connection with a 
preferred embodiment and method of use thereof, it will be understood that 
it is not intended to limit the invention to that embodiment or method of 
use. On the contrary, it is intended to cover all alternatives, 
modifications and equivalents that may be included within the spirit and 
scope of the invention as defined by the appended claims. 
DETAILED DESCRIPTION OF THE INVENTION 
For a general understanding of the features of the present invention, 
reference numerals have been used throughout to designate identical 
elements. FIG. 1 schematically depicts the various elements of an 
illustrative color electrophotographic printing machine incorporating the 
present invention therein. It will become evident from the following 
discussion that the present invention is equally well suited for use in a 
wide variety of printing machines and is not necessarily limited in its 
application to the particular embodiment depicted herein. 
Inasmuch as the art of electrophotographic printing is well known, the 
various processing stations employed in the FIG. 1 printing machine will 
be shown hereinafter schematically and their operation described briefly 
with reference thereto. 
Turning now to FIG. 1, there is shown a color document imaging system 
incorporating the present invention. The color copy process can begin by 
inputting a computer generated color image into the image processing unit 
44. A digital signals which represent the blue, green, and red density 
signals of the image are converted in the image processing unit into four 
bitmaps: yellow (Y), cyan (C), magenta (M), and black (Bk). The bitmap 
represents the value of exposure for each pixel, the color components as 
well as the color separation. Image processing unit 44 may contain a 
shading correction unit, an undercolor removal unit (UCR), a masking unit, 
a dithering unit, a gray level processing unit, and other imaging 
processing sub-systems known in the art. The image processing unit 44 can 
store bitmap information for subsequent images or can operate in a real 
time mode. 
The photoconductive member, preferably a belt of the type which is 
typically multilayered and has a substrate, a conductive layer, an 
optional adhesive layer, an optional hole blocking layer, a charge 
generating layer, a charge transport layer, and, in some embodiments, an 
anti-curl backing layer. It is preferred that the photoconductive imaging 
member employed in the present invention be infrared sensitive. This 
allows improved transmittance through cyan image. Belt 100 is charged by 
charging unit 101a. Raster output scanner (ROS) 20a, controlled by image 
processing unit 44, writes a first complementary color image bitmap 
information by selectively erasing charges on the belt 100. The ROS 20a 
writes the image information pixel by pixel in a line screen registration 
mode. It should be noted that either discharged area development (DAD) can 
be employed in which discharged portions are developed or charged area 
development (CAD) can be employed in which the charged portions are 
developed with toner. After the electrostatic latent image has been 
recorded, belt 100 advances the electrostatic latent image to development 
station 103a. Liquid developer material is supplied by replenishing 
systems through tube 210 to development station 103a, fountain 16A 
advances a liquid developer material 13a from the chamber of housing 14a 
to development zone 17a, where it meets roller 11, rotating. Roller 11 is 
electrically biased to generate a DC field, or AC field with DC offset 
just prior to the entrance to development zone 17a so as to disperse the 
toner particles substantially uniformly throughout the liquid carrier. The 
toner particles, disseminated through the liquid carrier, pass by 
electrophoresis to the electrostatic latent image. The charge of the toner 
particles is opposite in polarity to the charge on the photoconductive 
surface. 
After the image is developed it is conditioned at development station 103A. 
Development station 103a also includes porous roller 18a having porous 
outer skin. Roller 18a receives the developed image on belt 100 and 
conditions the image by reducing fluid content while inhibiting the offset 
of toner particles from the image, and by compacting the toner particles 
of the image. Thus, an increase in percent solids is provided to the 
developed image, thereby improving the stability of the developed image. 
Preferably, the percent solids in the developed image is increased to more 
than 20 percent solids. Porous roller 18a operates in conjunction with 
vacuum 19 (not shown) for removal of liquid from the roller. A roller (not 
shown), in pressure against the blotter roller 18a, may be used in 
conjunction with or in the place of the vacuum, to squeeze the absorbed 
liquid carrier from the blotter roller for deposit into a receptacle. 
Furthermore, the vacuum assisted liquid absorbing roller may also find 
useful application where the vacuum assisted liquid absorbing roller is in 
the form of a belt, whereby excess liquid carrier is absorbed through an 
absorbent foam layer. A belt used for collecting excess liquid from a 
region of liquid developed images is described in U.S. Pat. Nos. 4,299,902 
and 4,258,115, the relevant portions of which are hereby incorporated by 
reference herein. 
In operation, roller 18a rotates in direction 20 to impose against the 
"wet" image on belt 100. The porous body of roller 18a absorbs excess 
liquid from the surface of the image through the skin covering pores and 
perforations. Vacuum 19 located on one end of the central cavity of the 
roller, draws liquid that has permeated through roller 18a out through the 
cavity and deposits the liquid in a receptacle or some other location 
which will allow for either disposal or recirculation of the liquid 
carrier to the replenishing system of the present invention. Porous roller 
18a, discharged of excess liquid, continues to rotate in direction 21 to 
provide a continuous absorption of liquid from image on belt 100. The 
image on belt 100 advances to lamp 34a where any residual charge left on 
the photoconductive surface is extinguished by flooding the 
photoconductive surface with light from lamp 34a. 
The development takes place for the second color for example magenta, as 
follows: the developed latent image on belt 100 is recharged with charging 
unit 100a. The developed latent image is re-exposed by ROS 20b. ROS 20b 
superimposing a second color image bitmap information over the previous 
developed latent image. At development station 103B, roller 116b, rotating 
in the direction of arrow 12, advances a liquid developer material 13 from 
the chamber of housing 14 to development zone 17b. Fountain 16b positioned 
before the entrance to development zone 17b disperses the toner particles 
substantially uniformly throughout the liquid carrier. The toner 
particles, disseminated through the liquid carrier, pass by 
electrophoresis to the previous developed image. The charge of the toner 
particles is opposite in polarity to the charge on the previous developed 
image. Roller 18b receives the developed image on belt 100 and conditions 
the image by reducing fluid content while inhibiting the departure of 
toner particles from the image, and by compacting the toner particles of 
the image. Preferably, the percent solids is more than 20 percent, 
however, the percent of solids can range between 15 percent and 40 
percent. The image on belt 100 advances to lamps 34b where any residual 
charge left on the photoconductive surface is extinguished by flooding the 
photoconductive surface with light from lamp 34b. 
The resultant image, a multi layer image by virtue of the developing 
station 103a, 103b, 103c and 103d having black, yellow, magenta, and cyan, 
toner disposed therein advances to the intermediate transfer station. It 
should be evident to one skilled in the art that the color of toner at 
each development station could be in a different arrangement. The 
resultant image is electrostatically transferred to the intermediate 
member by charging device 111. The present invention takes advantage of 
the dimensional stability of the intermediate member to provide a uniform 
image deposition stage, resulting in a controlled image transfer gap and 
improved image registration. Further advantages include reduced heating of 
the recording sheet as a result of the toner or marking particles being 
pre-melted, as well as the elimination of electrostatic transfer of 
charged particles to a recording sheet. Intermediate member 110 may be 
either a rigid roll or an endless belt having a path defined by a 
plurality of rollers in contact with the inner surface thereof. The multi 
layer image is conditioned by blotter roller 120 which receives the multi 
level image on intermediate member 110 and conditions the image by 
reducing fluid content while inhibiting the departure of toner particles 
from the image, and by compacting the toner particles of the image. 
Blotter roller 120 conditions the multi layer so that the image has a 
toner composition of up to 50 percent solids. 
Subsequently, multi layer image, present on the surface of the intermediate 
member, is advanced through image liquefaction stage B. Within stage B, 
which essentially encompasses the region between when the toner particles 
contact the surface of member 110 and when they are transferred to 
recording sheet 26, the particles are transformed into a tackified or 
molten state by heat which is applied to member 110 internally or 
externally. Preferably, the tackified toner particle image is transferred, 
and bonded, to recording sheet 26 with limited wicking by the sheet. More 
specifically, stage B includes a heating element 32, which not only heats 
the external surface of the intermediate member in the region of transfuse 
nip 34, but because of the mass and thermal conductivity of the 
intermediate member, generally raises the outer wall of member 110 at a 
temperature sufficient to cause the toner particles present on the surface 
to melt. The toner particles on the surface, while softening and 
coalescing due to the application of heat from the exterior of member 110, 
maintain the position in which they were deposited on the outer surface of 
member 110, so as not to alter the image pattern which they represent. The 
member continues to advance in the direction of arrow 22 until the 
tackified toner particles reach transfusing stage C. At transfuse nip 34, 
the liquefied toner particles are forced, by a normal force N applied 
through backup pressure roll 36, into contact with the surface of 
recording sheet 26. Moreover, recording sheet 26 may have a previously 
transferred toner image present on a surface thereof as the result of a 
prior imaging operation, i.e. duplexing. The normal force N, produces a 
nip pressure which is preferably about 100 psi, and may also be applied to 
the recording sheet via a resilient blade or similar spring-like member 
uniformly biased against the outer surface of the intermediate member 
across its width. 
As the recording sheet passes through the transfuse nip the tackified toner 
particles wet the surface of the recording sheet, and due to greater 
attractive forces between the paper and the tackified particles, as 
compared to the attraction between the tackified particles and the 
liquid-phobic surface of member 110, the tackified particles are 
completely transferred to the recording sheet as image marks. Furthermore, 
as the image marks were transferred to recording sheet 26 in a tackified 
state, they become permanent once they are advanced past transfuse nip and 
allowed to cool below their melting temperature. The transfusing of 
tackified marking particles has the further advantage of only using heat 
to pre-melt the marking particles, as opposed to conventional heated-roll 
fusing systems which must not only heat the marking particles, but the 
recording substrate on which they are present. 
After the developed image is transferred to intermediate member 110, 
residual liquid developer material remains adhering to the photoconductive 
surface of belt 100. A cleaning roller 31 formed of any appropriate 
synthetic resin, is driven in a direction opposite to the direction of 
movement of belt 100 to scrub the photoconductive surface clean. It is 
understood, however, that a number of photoconductor cleaning means exist 
in the art, any of which would be suitable for use with the present 
invention. Any residual charge left on the photoconductive surface is 
extinguished by flooding the photoconductive surface with light from lamp 
34d. 
Now referring to the replenishing system of the present invention for 
illustrative clarity one replenishing system is shown connected to supply 
vessel 200, however supply vessels 200a, 200b and 200c have separated 
replenishing system (not shown) connected thereto. FIG. 2 illustrates an 
embodiment of the invention wherein supply vessel 200 contains a liquid 
developer consisting essentially of (A) a nonpolar carrier liquid having a 
Kauri-butanol value of less than 30 and a high vapor pressure, (B) a 
nonpolar carrier liquid having a Kauri-butanol value of less than 30 a low 
vapor pressure. The mixture of carrier liquids (A and B) contains from 
about 50 to about 75 weight percent of the high vapor pressure fluid, and 
from about 50 to about 25 weight percent of the low vapor pressure fluid, 
(C) thermoplastic resin particles (toner particles) having a median 
particle size (volume weighted) less than 15 .mu.m, and with 90% of the 
particles (volume weighted) less than 30 .mu.m which optionally may 
contain a dispersed colorant, and (D) a charge director compound, the 
percent of solids in the developer being abut 0.5 to 6% by weight based on 
the total weight of liquid developer. The liquid electrostatic developer 
may contain unspecified components that do not prevent the advantage of 
the liquid developer from being realized. The replenishment system enables 
the concentration of solids in the liquid developer to be maintained in 
the range of about 0.5 to 6% by weight, based on the total weight of 
liquid developer, using a liquid developer contained in supply vessel 200. 
The carrier liquids and developer solids concentration in supply vessel 200 
are monitored by Fourier transform (ft) ir spectroscopy monitoring system. 
The (ft) ir spectroscopy monitoring system is movable by means of a motor 
and a controller (not shown) between monitoring cells 2, 2a, 2b, 2c of 
their respective supply vessels. Each monitoring cells comprises an 
infrared transmitting substance such as halide salt crystals; NaCl, KBr, 
etc. or other infra-red transmitting materials such as germanium or 
silicon wafer. The cell gap should be in the range of 0.015 to 1.0 mm. 
The FTIR spectroscopy monitoring system operates as follows: Infrared 
radiation from the source (1) is collimated and is directed through the 
optical path of the spectrometer. It is first directed through a Michelson 
interferometer, then it is focused on and transmits through the sample (in 
monitoring cell 2) and finally is focused on an infrared detector 3. The 
Michelson interferometer is a device that can divide a beam of radiation 
into two paths and then recombine the two beams after a path difference 
has been introduced. This creates a condition under which interference 
between the two beams can occur. Variations in intensity of the beam 
emerging from the interferometer can be measured as a function of path 
difference by a detector. The Michelson interferometer has two mutually 
perpendicular plane mirrors 4 and 5, one of which is moved at a constant 
velocity along an axis perpendicular to its plane. A beamsplitter 6 is 
positioned between the fixed and movable mirrors such that a beam of 
radiation from an external source can be partially reflected to the fixed 
mirror (4) and partially transmitted to the movable mirror (5). A 
difference in path length is introduced and as a consequence, the two 
beams interfere when they return to the beamsplitter. Because of this 
interference, the intensity of the two beams passing to the detector 
depends on the difference in path length of the beams in the two arms of 
the interferometer. This intensity variation at the detector ultimately 
yields the spectral information in a Fourier transform spectrometer. 
Monochromatic radiation produces a cosine wave as the optical paths are 
varied while a polychromatic source produces an interferogram, or time 
domain spectrum, which is simply a superposition of all the cosine waves 
corresponding to the individual frequency components present. The infrared 
spectrum is calculated from this interferogram by computing the cosine 
Fourier transform. 
The present invention employs the P-matrix to calculate the concentrations 
from infrared absorption of carbon hydrogen stretching frequencies of 
individual developer components. The P-matrix has been described in Brown, 
C. W. "Multicomponent infrared analysis using P-matrix methods", J. Test. 
Eval 12, 86 (1984) the disclosure of which is totally incorporated herein 
by reference. The P-matrix changes the formulation of Beer's law to: 
EQU C=PA 
where: 
C is the matrix of concentrations 
P is the matrix relating absorbance to concentration 
A is the matrix of absorbances 
In operation, a set of standands is run with developer components having 
known concentrations. From that the absorbance data the P matrix is 
calculated: 
EQU P=CA'(AA').sup.-1 
Then, when an unknown monitoring cell of a vessel is run, the 
concentrations can be found immediately: 
EQU C=PA 
Specific embodiments of the invention will now be described in detail. 
These examples are intended to be illustrative, and the invention is not 
limited to the materials, conditions, or process parameters set forth in 
these embodiments. All parts and percentages are by weight unless 
otherwise indicated. Comparative Examples are also provided. 
EXAMPLE 1 
Below is an example of the application of this method to a two component 
carrier fluid. 
TABLE 1 
______________________________________ 
Comparison of Actual weight % versus FTIR 
Multicomponent Analysis weight % of Individual Components 
in Mixed LID Carrier Fluids. 
Test Actual % Analytical % 
Solu- 
Isopar- Norpar- 
Isopar- Norpar- 
tion L Superla 15 L Superla 
15 
______________________________________ 
A 50.0 50.0 -- 50.2 49.8 -- 
B 75.0 25.0 -- 75.6 24.4 -- 
______________________________________ 
EXAMPLE 2 
This method extended to three component carrier fluids. 
TABLE 2 
______________________________________ 
Comparison of Actual weight % versus FTIR 
Multicomponent Analysis weight % of Individual Components 
in Mixed LID Carrier Fluids. 
Test Actual % Analytical % 
Solu- 
Isopar- Norpar- 
Isopar- Norpar- 
tion L Superla 15 L Superla 
15 
______________________________________ 
C 65.0 30.0 5.0 65.3 30.4 4.2 
______________________________________ 
The ingredients for the liquid developer are obtained from at least one 
liquid toner concentrate vessel 202 that contains aggregates of 
thermoplastic resin particles having a median particle size (volume 
weighted) greater than 15 .mu.m, with 90% of the particles (volume 
weighted) not less than 30 .mu.m. The concentrate is composed of 30 to 
100% by weight of such particles and to 70% by weight nonpolar liquid (A 
or B). Vessel 203 contains liquid component (A). Vessel 204 contains 
liquid component (B). Vessel 205 contains unknown concentration reclaimed 
mixture of liquid components (A and B). Means 206, 207, 208 and 209 
respectively communicate with concentrate vessel 202 and liquid vessels 
203, 204, 205 connecting said vessels with dispersing vessel 6 in order to 
supply vessel 6 with liquid toner concentrate from vessel 202 and nonpolar 
liquid from vessels 203, 204, 205. Communicating means 206, 207, 208 and 
209 can be pipes, tubes, conduits, or the like, through which the toner 
concentrate and nonpolar liquid are supplied and metered (by means not 
shown) into vessel 6. Metering devices can be solenoid metering pumps, 
piston pumps, metered feed screws, peristaltic pumps, diaphragm pumps, or 
other metering devices selected on the basis of the physical 
characteristics of the material being transported. Metering devices are 
responsive to the monitoring system so that liquid developer can be 
adjusted to have desired concentration of each component in vessel 200. 
Dispersing vessel 6 contains means for providing an electric field as shown 
in FIG. 2 as described in U.S. application Ser. No. 08/317,009 (D/94171) 
entitled "SYSTEM FOR REPLENISHING ELECTROSTATIC LIQUID DEVELOPERS", the 
disclosure of which is totally incorporated herein by reference. Vessel 6 
comprises two conductive plates 312 and 314 separated at the perimeter by 
an insulator 316. Conductive plates 312 and 314 are connected to voltage 
supply 310. When voltage is supplied to the plates 312 and 314, an 
electric field is transmitted through dispersing vessel 6, which enable 
agglomerates of the ink or developer to break apart or fracture thereby 
providing for the efficient desirable dispersion of the ink solids in the 
ink carrier fluids. 
Means 8, communicating with dispersing vessel 6, connects the vessel with 
supply vessel 200 containing the liquid developer to be replenished. 
Communicating means 8 can be pipes, tubes, conduits, or the like, through 
which the dispersed toner particles are supplied and metered (by means not 
shown) into said vessel as required to maintain the developer solids 
concentration in vessel 200 as measured by the solids concentration sensor 
(not shown). The metering device can be solenoid metering pumps, metered 
feed screws, peristaltic pumps, piston pumps, diaphragm pumps, or other 
metering characteristics of the material being transported. 
At least one of supply vessel 200, liquid toner concentrate vessel 202 or 
liquid vessel 203, can contain a charge director compound, more fully 
described below, in an amount of 0.1 to 1000 milligrams per gram of 
developer solids, preferably 1 to 300 milligrams per gram of developer 
solids. The specific ingredients used to make up the composition of the 
liquid electrostatic developer are described more fully as follows. 
Examples of high pressure liquid carriers selected for the developers of 
the present invention include a liquid with viscosity of from about 0.5 to 
about 500 centipoise, preferably from about 1 to about 20 centipoise, and 
a resistivity greater than or equal to about 5.times.10.sup.9 
ohm/centimeters, such as 10.sup.13 ohm/centimeters, or more, such as a 
branched chain aliphatic hydrocarbon, like the ISO.RTM. series, 
available from the Exxon Corporation. These hydrocarbon liquids are 
considered narrow portions of isoparaffinic hydrocarbon fractions with 
extremely high levels of purity. For example, the boiling range of ISO 
G.RTM. is between about 157.degree. C. and about 176.degree. C.; ISO 
H.RTM. is between about 176.degree. C. and about 191.degree. C.; ISO 
K.RTM. is between about 177.degree. C. and about 197.degree. C.; ISO 
L.RTM. is between about 188.degree. C. and about 206.degree. C.; ISO 
M.RTM. is between about 207.degree. C. and about 254.degree. C.; and 
ISO V.RTM. is between about 254.degree. C. and about 329.degree. C.; 
ISO L.RTM. has a mid-boiling point of approximately 194.degree. C.; 
ISO M.RTM. has an auto ignition temperature of 338.degree. C. ISO 
G.RTM. has a flash point of 40.degree. C. as determined by the tag closed 
cup method; ISO H.RTM. has a flash point of 53.degree. C. as determined 
by the ASTM D-56 method; ISO L.RTM. has a flash point of 61.degree. C. 
as determined by the ASTM D-56 method; and ISO M.RTM. has a flash point 
of 80.degree. C. as determined by the ASTM D-56 method. The liquids 
selected are known and should have an electrical volume resistivity in 
excess of about 10.sup.9 ohm-centimeters and a dielectric constant below 
or equal to 3.0. Moreover, the vapor pressure at 25.degree. C. should be 
less than or equal to 10 Torr in embodiments. 
Examples of low vapor pressure carrier fluids, or liquids include the 
NOR.RTM. series available from Exxon Corporation, the SOLTROL.RTM. 
series from the Phillips Petroleum Company, and the SHELLSOL.RTM. series 
from the Shell Oil Company can be selected. 
The amount of the liquid employed in the developer of the present invention 
is from about 90 to about 99.9 percent, and preferably from about 95 to 
about 99 percent by weight of the total developer dispersion. The total 
solids content of the developers is, for example, 0.1 to 10 percent by 
weight, preferably 0.3 to 3 percent, and more preferably, 0.5 to 2.0 
percent by weight. 
The toner particles can be any colored particle compatible with the liquid 
medium, such as those contained in the developers disclosed, for example, 
in U.S. Pat. Nos. 3,729,419; 3,841,893; 3,968,044; 4,476,210; 4,707,429; 
4,762,764; and 4,794,651; and U.S. application Ser. No. 08/268,608 the 
disclosures of each of which are totally incorporated herein by reference. 
The toner particles can consist solely of pigment particles, or may 
comprise a resin and a pigment; a resin and a dye; or a resin, a pigment, 
and a dye. Suitable resins include poly(ethyl acrylate-co-vinyl 
pyrrolidone), poly(N-vinyl-2-pyrrolidone), and the like. Other examples of 
suitable resins are disclosed in U.S. Pat. No. 4,476,210, the disclosure 
of which is totally incorporated herein by reference. Suitable dyes 
include Orasol Blue 2GLN, Red G, Yellow 2GLN, Blue GN, Blue BLN, Black CN, 
Brown CR, all available from Ciba-Geigy, Inc., Mississauga, Ontario, 
Morfast Blue 100, Red 101, Red 104, Yellow 102, Black 101, Black 108, all 
available from Morton Chemical Company, Ajax, Ontario, Bismark Brown R 
(Aldrich), Neolan Blue (Ciba-Geigy), Savinyl Yellow RLS, Black RLS, Red 
3GLS, Pink GBLS, all available from Sandoz Company, Mississauga, Ontario, 
and the like. Dyes generally are present in an amount of from about 5 to 
about 30 percent by weight of the toner particle, although other amounts 
may be present provided that the objectives of the present invention are 
achieved. Suitable pigment materials include carbon blacks such as 
Microlith.RTM. CT, available from BASF, Printex.RTM. 140 V, available from 
Degussa, Raven.RTM. 5250 and Raven.RTM. 5720, available from Columbian 
Chemicals Company. Pigment materials may be colored, and may include 
magenta pigments such as Hostaperm Pink E (American Hoechst Corporation) 
and Lithol Scarlet (BASF), yellow pigments such as Diarylide Yellow 
(Dominion Color Company), cyan pigments such as Sudan Blue OS (BASF), and 
the like. Generally, any pigment material is suitable provided that it 
consists of small particles and that it combines well with any polymeric 
material also included in the developer composition. Pigment particles are 
generally present in amounts of from about 5 to about 40 percent by weight 
of the toner particles, and preferably from about 10 to about 30 percent 
by weight. The toner particles should have an average particle diameter 
from about 0.2 to about 10 microns, and preferably from about 0.5 to about 
2 microns. The toner particles may be present in amounts of from about 1 
to about 10, and preferably from about 2 to about 4 percent by weight of 
the developer composition. 
Examples of suitable charge control agents include lecithin (Fisher Inc.); 
OLOA 1200, a polyisobutylene succinimide available from Chevron Chemical 
Company; basic barium petronate (Witco Inc.); zirconium octoate (Nuodex); 
aluminum stearate; salts of calcium, manganese, magnesium and zinc; 
heptanoic acid; salts of barium, aluminum, cobalt, manganese, zinc, 
cerium, and zirconium octoates; salts of barium, aluminum, zinc, copper, 
lead, and iron with stearic acid; and the like. The charge control 
additive may be present in an amount of from about 0.01 to about 3 percent 
by weight, and preferably from about 0.02 to about 0.05 percent by weight 
of the developer composition. 
It is, therefore, evident that there has been provided, in accordance with 
the present invention, a replenishing system that fully satisfies the aims 
and advantages hereinbefore set forth. While this invention has been 
described in conjunction with one embodiment thereof, it is evident that 
many alternatives, modifications and variations will be apparent to those 
skilled in the art. Accordingly, it is intended to embrace all such 
alternatives, modification and variations as fall within the spirit and 
broad scope of the appended claims.