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Description  |
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BACKGROUND OF THE INVENTION
This invention relates to imaging systems and more particularly to liquid
development systems and liquid developers for use in color reproduction
utilizing multiple development.
Color electrophotography with multiple development is capable of producing
color reproductions by the following exemplary procedures. A suitable
photoconductor such as substantially white zinc oxide photosensitive
paper, Electrofax paper for example, is electrostatically uniformly
charged in the dark and then exposed through a green filter to an
imagewise projection of a color image to form an electrostatic latent
image on the photoconductor. The electrostatic latent image is then
developed with magenta colored toner to form a magenta colored image
corresponding to said electrostatic latent image. The zinc oxide
photosensitive paper is again electrostatically uniformly charged in the
dark and then exposed through a red filter to an imagewise projection of a
colored image in register with said magenta developed image to form a
second electrostatic latent image, which second image is developed with
cyan colored toner. Similarly, the zinc oxide photosensitive paper is
again electrostatically uniformly charged in the dark and then exposed
through a blue filter to an imagewise projection of a colored image in
register with said magenta and cyan developed images to form a third
electrostatic latent image, which is then developed with yellow toner to
complete a reproduced color image.
The sequence of exposures through colored filters in this multiple
development process may be performed in any suitable sequence other than
the green, red and blue sequence recited above. A significant drawback of
this multiple development process is that after the formation of the image
of the first color and during the second imaging sequence consisting of
uniformly charging and imagewise exposing followed by development with
tonor of the second color, the zinc oxide photosensitive paper is apt to
be electrostatically charged more strongly in the portion where said first
colored image is formed in comparison with the other portion where such
image does not exist. In addition, the portion of the zinc oxide paper
where the first colored image is formed is apt to retain charge in
nonimage areas when imagewise exposed to a light pattern which is capable
of neutralizing the electrostatic charge in the latter portion. This
retained potential, which usually ranges from several volts to several
tens of volts, arises from the fact that the ion absorbed by the toner
during charging is not neutralized during the imagewise exposure to light.
Since the toner usually consists of electrically insulating material the
neutralization of the ion for example, held by the toner layer, for
material the corona ion generated by corona discharge is hindered.
Electroconductive toner cannot be employed in electrophotography with
multiple development since the portion of the photoconductor having such
toner on its surface during the second and third imaging sequences cannot
bear electrostatic charge.
Furthermore, when the electrostatic charge on the first toner layer is not
completely neutralized, the toner of second color tends to be improperly
deposited onto the first toner layer, giving rise to impure color
formation. Similar difficulties also arise in the development with the
toner of the third color, and the tendency for improper toner deposition
increases as the reflective optical density of the toner image already
present is increased. The result of these characteristics is that it is
very difficult to obtain color reproduction of satisfactory quality.
These difficulties have been lessened to some degree by the use of the
techniques and materials disclosed in U.S. Pat. No. 3,060,020 which is
herein incorporated by reference. Essentially therein disclosed is a
technique utilizing toner chiefly consisting of photoconductive zinc oxide
powder in order to provide appropriate photoconductive property to the
toner image. This technique may be more fully understood by reference to
FIGS. 1, 2A and 2B of the accompanying drawing in which:
FIG. 1 is an enlarged cross section of the toner particles.
FIG. 2A is an enlarged cross section of a toner image on an imaging
surface.
FIG. 2B is an enlarged cross section of a fused toner image on an imaging
surface.
In FIG. 1, toner particle 10 consists of core 11 composed of
photoconductive zinc oxide particle surrounded by a colored resin layer
13, which may be composed either of pigment particles 12 dispersed in
resin as shown or of resin colored with an appropriate dye. The resin 13
is required to be liquified by heat, and the melting point thereof is
usually required to lie between about 90 and about 250.degree. C. In
addition, the resin layer is required to be highly insulting and to have
sufficient capability to generate favorable frictional electricity (i. e.
a capability to generate sufficiently strong positive charge if the latent
image is negative). Furthermore the resin 13, when melted, should be of
sufficiently low viscosity, preferably between about 45 and about 10,000
centipoises, so as to be removed from the surface of the zinc oxide core.
FIGS. 2A and 2B show the method of using the dry powder toner described in
said U.S. Patent in a dry development system. As shown in FIG. 2A, the
toner image 21 is formed by toner particles 10 held onto the imaging
surface 22 bearing an electrostatic latent image. The toner layer thus
formed simply by means of electrostatic forces of attraction does not
possess photoconductivity due to the high electric resistance of resin
layer 13 surrounding the zinc oxide core 11. When the toner is melted by
heat as shown in FIG. 2B, the resin 13 together with pigment 12 is spread
onto the imaging surface thereby exposing the surface of zinc oxide core
particle. As a result, the fixed toner layer 21' shown in FIG. 2B acquires
photoconductive property on account of the exposed zinc oxide particles
11.
This process, however, has several drawbacks among which are the fact that
the heating up to 90-250.degree. C. required for melting the toner image
may cause irreversible dilatation of the imaging surface which may result
in the formation of unsatisfactory prints due to imperfect registration
during the second and third imaging sequences. This difficulty is
especially pronounced when the support material consists of paper, as for
example in Electrofax paper. In addition, the colors obtained by this
process are not of high saturation but rather become whitish since the
white zinc oxide powder is almost exposed to the surface after fixing of
the toner image by heat. This difficulty results in impure color or lack
of color density when three color images are superimposed one upon the
other. The melting point and limited viscosity range of the resin
seriously confine the selection of suitable materials to only certain
types which also must be highly insulating and capable of being
triboelectrically charged to a suitable polarity and potential.
Furthermore, this dry developer toner cannot be used with a particle size
smaller than a certain limit, and therefore is not capable of providing
high resolution and satisfactory tone reproduction. Actually, the toner is
frequently composed of aggregates of several to several tens of zinc oxide
particles instead of being composed of a single particle as shown in the
ideal case of FIG. 1.
SUMMARY OF THE INVENTION
It is therefore an object of this invention to provide a novel liquid
developer.
It is another object of this invention to provide a novel liquid developer
for use in color electrophotography with multiple development.
It is another object of this invention to provide a liquid developer
containing photoconductive particles.
It is another object of this invention to provide a novel imaging system.
It is another object of this invention to provide an imaging system capable
of high resolution and high color density.
It is another object of this invention to provide a color
electrophotographic process with multiple development wherein the toner
particles do not have to be fused to the imaging surface.
The above objects and others are accomplished generally speaking by
providing an imaging system employing a liquid developer comprising a
suspension in an insulating liquid of colored particles and white or dye
sensitized photoconductive particles preferably in the presence of a
dissolved or dispersed resin or oil for regulating the electrostatic
charge or for stabilizing the suspension. In the liquid development
technique with multiple development the surface bearing the electrostatic
latent image after the development step of the first imaging sequence has
been completed is subjected before contacting with the developer of the
next imaging sequence to a step of pre-bathing in which said image bearing
surface is brought into contact with a highly insulating liquid not
containing toner in order to neutralize the electrostatic charge remaining
in the toner layer from the development step of the previous imaging
sequence to thereby prevent fogging of the several toner images. The
pre-bathing step may be accomplished immediately after the development
step or it may be accomplished prior to the development step in the second
and third imaging sequences or it may be accomplished prior to the second
and third exposure steps.
The invention may be more fully understood by reference to FIGS. 3, 4 and 5
of the accompanying drawing in which:
FIG. 3 is an enlarged cross section of the toner and photoconductive
particles of this invention.
FIG. 4 is a cross section of a developed image formed by development with
the liquid developer of this invention.
FIG. 5 is a graph showing the change in electrostatic charge on the toner
image of FIG. 2.
The developer of this invention comprises toner particles and
photoconductive particles suspended in an insulating liquid.
The solids of the developer, generally represented in cross section in FIG.
3, comprise photoconductive particle 37, preferably consisting of
particulate photoconductive material 33 and thin layer of resin 32
absorbed therearound.
The resin layer 32 is required to be as thin as possible to facilitate
adequate exposure of photoconductive material 33 to dissipate any charge
thereon. Otherwise, it would be necessary to employ some means to remove
the resin layer to expose photoconductive particle 33. As disclosed in the
following examples to provide adequate exposure, the resin covering the
photoconductive particles is preferably soluble in the carrier liquid of
the liquid developer. The resin layer may be employed in any suitable
amount. Typically, the dispersed particle usually contains not more than
about 2 parts by weight of the resin in 100 parts of particulate
photoconductive material. The photoconductive properties of the particle
are hardly affected by the presence of this amount of resin and the
electrostatic charge on the developed toner layer containing said
particles is capable of being completely neutralized without the
troublesome additional steps of removing the resin layer as indicated in
the aforementioned U.S. Patent. Any suitable resin may be employed to
provide a thin layer on a suitable particulate photoconductive material.
Typical well known particulate photoconductive materials include zinc
oxide, zinc sulfide, cadmium sulfide, zinc selenide, cadmium selenide,
titanium dioxide, zinc cadmium sulfide, zinc magnesium oxide,
phthalocyanine, and polyvinyl carbazole. Typical resins that may be
employed to provide the resin layer include epoxy ester resin, silicone
resin, alkyd resin, phenol-formaldehyde resin, xylen-formaldehyde resin
etc.
Toner particle 34, composed of colored particle 36 and preferably having a
layer of a resin 35 absorbed therearound, determines the color of the
developed image, and provides higher saturation of color as the diameter
thereof decreases. The color of the developed toner image also acquires
higher saturation as the amount of particles 34 increases with respect to
that of particles 37 but the photoconductive property of toner layer is
simultaneously deteriorated to provide satisfactory balance between color
and photoconductivity the ratio between the amounts of particles 37 and
particles 34 should be controlled within a suitable range. Although this
range is dependent to some extent on the sizes of both particles,
typically from about 5 to about 104 parts by weight of photoconductive
particles 37 are used for every 100 parts by weight of toner particles 34,
for typical particle sizes of particles 37 and 34 of from about 0.1 to
about 1micron and from about 0.01 to about 0.5 micron respectively. The
toner particle 34 may comprise any suitable colorant from the group of
well known dyes and pigments. Typically in multiple development color
electrophotography three liquid developers are provided each one
containing one of the three subtractive primaries yellow, magenta and
cyan. Typical well known specific colorants lacking photoconductive
properties include benzidine yellow, carmine, millory blue, rhodamine,
titanium yellow and Hansa yellow. When the colorant is an organic dye it
is preferably insoluble in the carrier liquid and since the specific
gravities of usual organic dyes and typical photoconductors such as zinc
oxide are from about 1.5 to about 2 and about 5.6 respectively, the above
weight ratio can be converted into 1.3-3500 parts by volume of zinc oxide
particles 33 with respect to 100 parts by volume of dye particles 36, with
the amount of resin 32 and 35 around the core particles 33 and 36 being
neglected. Zinc oxide present in excess of this range will result in
unfavorable color reproduction whereas the toner layer will show
insufficient photoconductivity if the amount of zinc oxide does not reach
this range.
Any suitable well known insulating liquid may be employed as the vehicle
for the photoconductive particles and toner particles. Typical well known
materials have volume resistivities greater than about 10.sup.10 ohm-cm so
as not to affect the electrostatic charge pattern on the insulating layer
and low dielectric constants of less than about 3.4. Typical specific
vehicles include among others, the nonpolar hydrocarbons and hydrocarbon
derivates such as benzene, kerosene, cyclohexane, toluene and carbon
tetrachloride.
In FIG. 2A, the toner layer shows high electric resistance as the layer is
composed of toner particles 10 electrically insulated from each other,
whereas in FIG. 4 the electric carrier formed by the effect of light in
the photoconductive particles 37 can easily unite with ions on toner
particles present in the proximity of said particles 37 due to the uniform
distribution of photoconductive particles 37 and toner particles 34 and
the smaller distance between said photoconductive particles 37.
Consequently, in the process of this invention, it is completely
unnecessary to melt the toner layer by heat to expose the photoconductive
particles. The present invention differs from the technique described with
respect to FIGS. 1 and 2 in that the electrostatic charge remaining on the
developed toner layer can be completely neutralized prior to development
in the second or third development step simply by contacting said layer
with an insulating liquid. In the liquid development technique with
multiple development the image bearing surface after the first development
step has been completed is subjected before contacting with the developer
of the next development step to a step of pre-bathing in which said
surface is brought into contact with a highly insulating liquid not
containing toner in order to neutralize the electrostatic charge still
remaining in the toner layer from the previous development sequence. The
sequence of steps in this multiple development technique may include
initial charging and exposure of the photoconductor through a suitable
first filter followed by development with the appropriately colored liquid
developer of this invention. The photoconductor with the first developed
toner image thereon is subjected to the pre-bathing technique of this
invention prior to the second imaging sequence comprising charging,
exposing through an appropriate filter and developing with the
corresponding colored liquid developer. After this second development
sequence the photoconductor bearing the first and second deveoped toner
image is subjected to an additional pre-bathing technique prior to the
development step of the third imaging sequence. While the above technique
describes the pre-bathing step as the initial step in the second and third
imaging sequence, it is necessary only that the photoconductor be
subjected to the pre-bathing technique prior to the development step in
the second and third imaging sequence. In this manner, any residual charge
remaining on the imaging surface from a prior imaging sequence is
effectively neutralized prior to subsequent deposition of toner in
response to an electrostatic charge pattern. Therefore, toner is
electrostatically attracted to only the image areas produced in each
imaging sequence and is not deposited on the photoconductor in response to
more than one or overlapping image areas of several imaging sequences. To
provide this result, the photoconductor may be subjected to the
pre-bathing treatment prior to charging, exposure or development in the
second and third imaging sequence.
During uniform electrostatic charging in the dark the zinc oxide
photosensitive paper as shown in the toner layer depicted in FIG. 4 is
electrostatically charged by the adsorption of ions. As shown in FIG. 5,
the surface potential of toner layer reaches V.sub.1 by means of
electrostatic charging such as by corona discharge carried out for a
period between time O and t.sub.1 in the dark, and then decreases to
V.sub.2 by interrupting said charging at time t.sub.1 and effecting
imagewise exposure from the time t.sub.1 and t.sub.2. The proportion of
photoconductive particles 37 is preferably as small as possible since a
larger proportion thereof will inevitably result in the deterioration of
color quality although a larger portion will enable the attainment of a
lower value of V.sub.2 against a determined amount of light of exposure.
Successively the surface potential can be rapidly reduced to zero by
bringing the toner image into contact with the pre-bath liquid. This
neutralization of surface potential by pre-bath step provides a great
advantage of this invention in comparison with the process of aforesaid
U.S. Patent. The neutralization by means of the pre-bath step can be
explained by the formation of ions by the triboelectric contact between
the particles and pre-bath liquid, and also by the fact that the liquid
filling the gap between the particles give mobility to the ions.
An additional advantage of this invention lies in the fact that the ratio
between the amounts of pigment particles 34 and photoconductive particles
37 can be arbitrarily varied during or prior to use of the developer,
whereas in the process disclosed in U.S. Patent this ratio is fixed when
the developer is prepared. When reproducing colored positive image from a
colored positive original pattern onto a panchromatically sensitized
photosensitive layer by means of the multiple development process, it is
necessary to select the order of development in order to minimize the
effect of undesirable spectral absorption of available dyes or pigments of
cyan, magenta and yellow. Since these dyes and pigments generally show
undesirable spectral absorption in the shorter wavelength side with
respect to the main absorption region thereof, it is preferred to provide
development in the order of shorter to longer wavelength region with
respect to the main absorption of these dyes or pigments, namely in the
order of yellow, magenta and cyan successively. At this point it is to be
noted that yellow-colored dyes or pigments generally have tendency to show
relatively high retentive potential. Consequently, the process of this
invention is particularly effective when applied in the liquid developer
containing yellow dye or pigment, and is capable of providing almost ideal
color reproduction.
DESCRIPTION OF PREFERRED EMBODIMENTS
The following preferred examples further define, describe and compare
preferred materials, methods and techniques of the present invention. In
the examples, all parts and percentages are by weight unless otherwise
specified.
EXAMPLE I
A yellow developer is prepared by dispersing the following material by
means of ultrasonic wave of 29 KC and 150 W to produce Solution A.
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Benzidine yellow 0.4 parts by weight
Styrenated-alkyd resin
0.5 parts by weight
Linseed oil 0.1 parts by weight
Cyclohexane 400.0 parts by weight
Kerosene 100.0 parts by weight
______________________________________
The following materials are dispersed by means of ultrasonic wave of 29 KC
and 150 W to form Solution B:
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Photoconductive zinc
oxide 0.1 part by weight
Styrenated-alkyd resin
0.5 part by weight
Linseed oil 0.1 part by weight
Cyclohexane 400.0 parts by weight
Kerosene 100.0 parts by weight
______________________________________
The developer of this invention may be prepared by mixing Solution A and
Solution B in a suitable ratio. The following table shows the values of
V.sub.1 and V.sub.2 for various mixing ratios, wherein t.sub.1 and t.sub.2
are 10 and 20 seconds respectively, and the photosensitive material is
exposed to white light of 400 lux at 1=t.sub.1 and is brought into contact
with kerosene at t=t.sub.2.
______________________________________
No. 1 2 3 4 5
______________________________________
Solution A 100CC 50 30 25 20
Solution B 0CC 50 70 75 80
V.sub.1 27V 35 32 25 20
V.sub.2 25V 25 19 13 13
V.sub.3 7V 0 0 0 0
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As can be seen from the above table, the value of V.sub.3 remains at 7
volts when photoconductive particles are not dispersed in the developer,
leading to impure color due to the improper attraction of other toner in
the succeeding development to these charged toner areas.
On the other hand, the presence of photoconductive particles in an
appropriate amount effectively reduces the value of V.sub.3 to zero, and
still the whitening of the yellow image obtained due to the adhering of
the white zinc oxide particles is hardly observable in the images
developed with the developers 2 through 5.
Although the Solution A and Solution B are prepared in diluted state at
first in this example, it is also possible to prepare the developer by
preparing a paste with linseed oil, zinc oxide powder and resin and then
dispersing the paste into dispersion media such as cyclohexane or kerosene
directly prior to use.
EXAMPLE II
The following materials are blended in a ball mill for one hour to give
Paste A:
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Brilliant carmine 6B 30 parts by weight
Varnish obtained by heating
1:1 mixture of linseed oil
and rosin denatured phenol-
formaldehyde resin 60 parts by weight
Linseed oil 10 parts by weight
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In a similar manner, Paste B is prepared of the following materials:
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Photoconductive zinc
oxide 20 parts by weight
Varnish 60 parts by weight
Linseed oil 20 parts by weight
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A developer obtained by dispersing about 1 gram of Paste A in 800 CC of
cyclohexane and 200 CC of kerosene provides a developed toner image having
a reflective optical density of about 2.0 and V.sub.1 and V.sub.3 are
found to be 8 and 3 volts respectively. On the other hand, V.sub.3 is
found to be zero in the toner images developed in the same manner with a
developer obtained by dispersing from about 0.1 to about 2.0 g of Paste B
into the above-mentioned developer. The whitening of obtained image due to
dispersed zinc oxide powder is hardly observable.
EXAMPLE III
A cyan developer is prepared by blending the following materials in a ball
mill for one hour to form Paste A:
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Millory blue 40 parts by weight
Varnish 50 parts by weight
Linseed oil 10 parts by weight
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Paste B is also prepared similarly from the following materials:
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Photoconductive zinc
oxide 20 parts by weight
Varnish 60 parts by weight
Linseed oil 20 parts by weight
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A developer prepared by dispersing 1 gram of Paste A in 800 CC of
cyclohexane and 200 CC of kerosene provides a developed toner image having
a reflective optical density of about 2.0 and V.sub.1 and V.sub.3 are
found to be 3 and 2 volts respectively. On the other hand, V.sub.3 is
reduced to zero in similar toner images developed by developers prepared
by dispersing from about 0.05 to about 2.0 g of Paste B into the
above-mentioned developer.
EXAMPLE IV
A yellow developer is prepared by the procedure of Example I except that
the white photoconductive zinc oxide powder in Example I is replaced by
pale yellow dye-sensitized zinc oxide powder, which has been prepared by
placing the zinc oxide particlces in the following composition for
sufficient time to cause absorption of dye onto the zinc oxide particles.
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White photoconductive
zinc oxide powder 10 grams
Titanium yellow 3 milligrams
Methanol 40 CC
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The zinc oxide particles are then separated by filtration and dried. The
sensitized zinc oxide thus obtained increases the photographic sensitivity
of the developer for white light more than 10 times, exhibits a lower
value of V.sub.2 due to its pale yellow color, and further improves the
color of toner itself. Sensitization with other sensitizing dyes can be
carried out in a similar manner.
The developers disclosed in Examples I through IV are suitable for exposure
with white light through a color separation negative image and are not
suitable for exposure directly from the colored original through a color
separation filter.
The following example provides a developer capable of use with direct
exposure from a colored original through a color separation filter.
EXAMPLE V
A yellow developer is prepared by dispersing the following materials by
means of ultrasonic wave for 10 minutes to obtain Solution A:
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Benzidine yellow 0.4 parts by weight
Varnish 0.4 parts by weight
Linseed oil 0.1 parts by weight
Cyclohexane 800.0 CC
Kerosene 200.0 CC
______________________________________
Similarly the following materials are dispersed by means of ultrasonic wave
for 10 minutes to obtain Solution B:
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Dye-sensitized
zinc oxide 0.2 parts by weight
Varnish 0.5 parts by weight
Linseed oil 0.1 parts by weight
Cyclohexane 800 CC
Kerosene 200 CC
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The liquid developer is prepared by mixing about equal parts Solution A and
Solution B. The dye sensitized zinc oxide is prepared by stirring 10 g of
photoconductive white zinc oxide powder having a particle size of from
about 0.1 to about 0.5 micron in a solution of the following formulation:
______________________________________
Rhodamin B 3 mg
Brilliant blue FCP 3 mg
Methanol 40 CC
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After 30 minutes the absorption of sensitizing dyes by the zinc oxide
powder, is terminated by separating the zinc oxide particles by
centrifuging and drying the separated zinc oxide particles. The zinc oxide
particles obtained are dyed a blue color and therefore stand in a
complementary relationship with yellow. Generally, if the zinc oxide is
dye-sensitized for a color (generally the color of light absorbed by the
colored particle) standing in complementary relationship with the color of
particle (yellow in this example), then the toner image obtained by the
first development shows photoconductivity against light of wavelength
region employed in the second and third exposure through appropriate color
separation filters. In this example, zinc oxide particles having absorbed
blue dyes are capable of showing photoconductivity against green and red
light.
In a similar manner, it is necessary to carry out the dye-sensitization of
zinc oxide with green dye when the first development is to be effected
with magenta toner, or with red dye when the first development is to be
effected with cyan toner.
Furthermore, when the first and second developments are to be carried out
respectively with yellow and magenta toner, then the zinc oxide contained
in the second toner should be sensitized with a dye having a color capable
of absorbing red light such as cyan, blue or green since the third
exposure should necessarily be carried out with red light.
Photoconductivity is not required for the toner used in the third
development sequence.
The generalization of this Example V leads to the fact that the first color
developer should be a highly insulating liquid in which are suspended
particles of said first color and photoconductive zinc oxide particles
sensitized with dye so as to show photoconductivity to the wavelength
region of light reflected from said first colored particles and that the
second color developer should be a highly insulating liquid in which
suspended are particles of a second color and photoconductive zinc oxide
particles sensitized with dye so as to show photoconductivity to the
wavelength region of light which is reflected by both the particles of the
first color and the second color.
EXAMPLE VI
A commercially available photoconductive insulating sheet comprising white
zinc oxide in an insulating film forming binder on a paper backing is
negatively charged in conventional manner and is exposed to a colored
original through a blue filter. The electrostatic latent image is
developed with the liquid developer described in Example V by immersing
the zinc oxide sheet in a bath of the developer. The zinc oxide sheet is
then charged in conventional manner and exposed while in registration with
the position during the first exposure to the same colored original
through a green filter. The zinc oxide sheet is uniformly contacted with
kerosene by immersing it in a bath of kerosene. The second electrostatic
latent image on the zinc oxide sheet is then developed by immersing the
sheet in a bath of the liquid developer described in Example II except
that the zinc oxide has been dye sensitized with brilliant green in a
manner similar to the dye sensitization described in Example V. The zinc
oxide sheet is again charged and exposed while in registration with the
position during the first and second exposures to the same color original
through a red filter. The zinc oxide sheet is then immersed in a bath of
kerosene. The third electrostatic latent image on the zinc oxide sheet is
then developed by contacting it with a dispersion of about one gram of
Paste A of Example III in 800 cubic centimeters of cyclohexane and 200
cubic centimeters of kerosene. The resulting color reproduction when
compared to the original is a faithful reproduction of the several color
image areas with good color density and with substantially no background.
It is readily realized from the foregoing discussion and exemplary
embodiments that the developer and processes of this invention provide
superior and unique reproducing capabilities. The developers of this
invention enable the reproduction of multicolor originals with exceptional
accuracy and substantially no undesirable overlapping of colors by forming
two or more color coded electrostatic latent images and developing the
images with a developer having toner particles of complementary color. The
color coded electrostatic latent images may be created by the use of color
separation negative images or exposure directly through a filter and
thereby enables exposure of the photoconductor to light of a selected
wavelength. The development of electrostatic latent images coded in
response to wavelength of light corresponding to the primary colors with
the liquid developers of this invention enables the reproduction of
multicolor images without the necessity of a toner fusing step and since
finer size particulate material may be employed produces reproductions of
superior quality.
Although specific materials and operational techniques are set forth in the
above exemplary embodiments using the developer composition and
development techniques of this invention, these are merely intended as
illustrations of the present invention. There are other developer
materials and techniques than those listed above which may be substituted
for those in the examples with similar results.
Other modifications of the present invention will occur to those skilled in
the art upon a reading of the present disclosure which modifications are
intended to be included within the scope of this invention.
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