U.S. patent number 3,582,205 [Application Number 04/821,564] was granted by the patent office on 1971-06-01 for imaging apparatus.
This patent grant is currently assigned to Xerox Corporation. Invention is credited to Leonard M. Carreira.
United States Patent |
3,582,205 |
Carreira |
June 1, 1971 |
IMAGING APPARATUS
Abstract
An apparatus for improving electrophoretic imaging by filling
the space between the electrodes of the electrophoretic imaging
system with an insulating liquid, then contacting the suspension
with the electrode and applying an electric field for imaging.
Inventors: |
Carreira; Leonard M. (Penfield,
NY) |
Assignee: |
Xerox Corporation (Rochester,
NY)
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Family
ID: |
27059682 |
Appl.
No.: |
04/821,564 |
Filed: |
May 5, 1969 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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519034 |
Jan 6, 1966 |
3485738 |
Dec 23, 1969 |
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Current U.S.
Class: |
399/131; 430/36;
430/32; 430/38 |
Current CPC
Class: |
G03G
17/04 (20130101) |
Current International
Class: |
G03G
17/04 (20060101); G03G 17/00 (20060101); G03g
015/00 () |
Field of
Search: |
;355/3,4 ;96/1.7,1
;204/181 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Matthews; Samuel S.
Assistant Examiner: Greiner; Robert P.
Parent Case Text
This is a division of application Ser. No. 519,034, filed Jan. 6,
1966, and now U.S. Pat. No. 3,485,738 issued on Dec. 23, 1969.
Claims
What I claim is:
1. An apparatus for electrophoretic imaging comprising:
a. at least two electrodes, at least one of which is a blocking
electrode movable relative to said other electrode,
b. a suspension of photosensitive pigment in a liquid carrier on a
first portion of said other electrode,
c. means to fill a gap between said blocking electrode and a second
portion of said other electrode with an insulating liquid,
d. means to apply an electric field between said electrodes,
and
e. means to simultaneously project an image on said suspension and
to move said blocking electrodes relative to said other electrode
in contact with said suspension.
2. The apparatus of claim 1 wherein one of said electrodes is at
least partially transparent.
3. An apparatus for electrophoretic imaging comprising in
combination:
a. a first electrode having a suspension of a photosensitive
pigment in a liquid carrier maintained on a first portion
thereof,
b. a second electrode capable of being a blocking electrode
maintained in near contact with a second portion of said first
electrode thereby providing a gap therebetween,
c. means to present an insulating liquid in a gap between said
second electrode and a second portion of said first electrode,
d. means to apply an electric field between said electrodes,
and
e. means to simultaneously project an image on said suspension and
to move said second electrode relative to said first electrode in
contact with said suspension.
4. The apparatus of claim 1 further including means to move said
electrodes relative to each other such that said second electrode
contacts the suspension on said first portion of said first
electrode while maintaining the insulating liquid therebetween.
5. Apparatus for electrophoretic imaging comprising in
combination:
a first electrode capable of supporting a suspension of
photosensitive pigment in a liquid carrier on a surface
thereof,
a second electrode capable of being a blocking electrode maintained
in at least near contact with said first electrode and being shaped
for providing a nip between said electrodes,
means to present an insulating liquid at the entrance to the nip
between said electrodes,
means to move said electrodes relative to each other whereby the
surfaces of the electrodes are traversed by the nip formed
therebetween,
means to simultaneously apply an electric field between said
electrodes, and
means to project an image on said suspension during the traversing
movement of said electrodes.
Description
This invention relates in general to imaging systems and, more
specifically, to an improved electrophoretic imaging system.
There has been recently developed an electrophoretic imaging system
capable of producing color images which utilizes electrically
photosensitive particles. This process is described in detail and
claimed in U.S. Pat. Nos. 3,384,565; 3,384,566 and 3,383,993 all
issued on May 21, 1968. In such an imaging system, variously
colored light-absorbing particles are suspended in a nonconductive
liquid carrier. The suspension is placed between electrodes,
subjected to a potential difference and exposed to an image. As
these steps are completed, selected particle migration takes place
in image configuration, providing a visible image at one or both of
the electrodes. An essential component of the system is the
suspended particles which must be electrically photosensitive and
which apparently undergo a net change in charge polarity upon
exposure to activating electromagnetic radiation, through
interaction with one of the electrodes. In a monochromatic system,
particles of a single color are used, producing a single colored
image equivalent to conventional black-and-white photography. In a
polychromatic system, the images are produced in natural color
because mixtures of particles of two or more different colors which
are each sensitive only to light of a specific wavelength or narrow
range of wavelengths are used. Particles used in this system must
have both intense and pure colors and be highly photosensitive.
Ordinarily, electrophoretic imaging systems include a transparent,
conductive injecting electrode upon which the dispersion of
photosensitive particles in an insulating liquid is coated. The
image to be reproduced is projected on the suspension to the
injecting electrode. During exposure, a potential, usually of from
300 to 2,000 volts is imposed on the suspension between the
injecting electrode and a relatively insulating blocking electrode.
This blocking electrode, ordinarily in the form of a roller or an
endless belt, consists of a conductive core with an insulating
surface. This blocking electrode is passed across the surface of
the liquid suspension during exposure. Unwanted photosensitive
particles migrate to the surface of the blocking electrode, leaving
an image on the injecting electrode corresponding to the
original.
It has often been found that images produced by the system broadly
described above have uneven density and are blotchy or mottled in
appearance. It is theorized that the uneveness in the image is
caused by varying corona discharge or air ionization between the
blocking electrode and the injecting electrode as the blocking
electrode approaches the particle suspension. While the system
described above is often capable of producing excellent images, at
times, especially during periods of high relative humidity, the
images produced are not of commercially acceptable quality. Thus,
there is a continuing need for improvements in image quality under
all ambient conditions.
It is, therefore, an object of this invention to provide an
electrophoretic imaging system which is devoid of the above-noted
disadvantages.
It is another object of this invention to provide a method of
eliminating varying corona discharge or air ionization between
electrodes in electrophoretic imaging systems.
It is another object of this invention to provide an
electrophoretic imaging system capable of producing images of
uniform density under varied humidity conditions.
The foregoing objects and others are accomplished in accordance
with this invention by filling the air gap between the electrodes
in an electrophoretic imaging system with an insulating liquid
before the electrodes are brought into proximity in the
image-forming area. The insulating liquid may comprise any material
which is sufficiently insulating to prevent corona discharge
between the electrodes and which is compatible with the insulating
liquid in which the imaging particles are suspended. Preferably,
the liquid should have a resistivity of about 10.sup.7
ohm/cm..sup.2 or greater. It is also preferred that the liquid have
the same general composition as the carrier liquid which the
photosensitive particles are suspended to ensure compatibility
should some of this liquid be carried by the roller into the
imaging area. Suitable insulating liquids include Sohio Odorless
Solvent 3440 (a kerosene fraction available from Standard Oil of
Ohio), Isopar G (a long chain-saturated aliphatic hydrocarbon
available from Humble Oil Company of New Jersey), Freon (a
fluorinated hydrocarbon available from E. I. Du Pont de Nemours and
Company), Fluorochemical FC-75 (a polyfluorinated mixture of
compounds containing eight carbon atoms, available from Minnesota
Mining and Manufacturing Co.), Silicon Fluid SF-96 (a dimethyl
silicane fluid available from General Electric), mineral oil,
decane, dodecane, N-tetradecane, molten paraffin, molten beeswax or
other molten thermoplastic material. Any other suitable insulating
liquid may be used where desired.
The advantages of this improved electrophoretic imaging system will
become further apparent upon consideration of the following
detailed disclosure of the invention; especially when taken in
conjunction with the accompanying drawing which shows a side view
of a simple exemplary for carrying out the process of this
invention.
Referring now to the FIGURE, there is seen a transparent electrode
generally designated 1 which, in this exemplary instance, is made
up of a layer of optically transparent glass 2 overcoated with a
thin optically transparent layer 3 of tin oxide, commercially
available under the name NESA glass. This electrode shall hereafter
be referred to as the "injecting electrode." Coated on the surface
of injecting electrode 1 is a thin layer 4 of finely divided
photosensitive particles disposed in an insulating liquid carrier.
The term "photosensitive" for the purpose of this invention, refers
to the properties of a particle which, one attracted to the
injecting electrode, will migrate away from it under the influence
of an applied electric field when it is exposed to actinic
electromagnetic radiation. For a detailed theoretical explanation
of the apparent mechanism of operation of this imaging process, see
the above mentioned U.S. Pats. Nos. 3,384,565; 3,384,566 and
3,383,993, the disclosures of which are incorporated herein by
reference. Adjacent to the liquid suspension 4 is a second
electrode 5 hereinafter called the "blocking electrode," which is
connected to one side of the potential source 6 through a switch 7.
The opposite side of potential source 6 is connected to the
injecting electrode 1 so that when switch 7 is closed, an electric
field is applied across the liquid suspension 4 between electrodes
1 and 5 as blocking electrode 5 passes over liquid suspension 4. An
image projection made up of light source 8, a transparency 9, and a
lens 10 is provided to expose the dispersion 4 to a light image of
the original transparency 9 to be reproduced. Electrode 5 is made
in the form of a roller having a conductive central core 11
connected to the potential source 6, The core is covered with a
layer of a blocking electrode material 12, which may be Baryta
paper or other suitable insulating material. The blocking electrode
may, of course, be in any other configuration capable of contacting
the suspension without relative movement at the suspension surface.
Typical alternative configurations are described in copending
application Ser. No. 452,651, filed May 3, 1965. The particle
suspension is exposed to the image to be reproduced while potential
is applied across the blocking and injecting electrodes by closing
switch 7. Roller 5 is caused to roll across the top surface of
injecting electrode 1 with switch 7 closed during the period of
image exposure. This light exposure causes exposed particles
originally attracted to electrode 1 to migrate through the liquid
and adhere to the surface of the blocking electrode 5, leaving
behind a pigment image on the injecting electrode surface which is
a duplicate of the original transparency 9. After exposure, the
relatively volatile carrier liquid evaporates off, leaving behind
the image. This process, utilizing only components exemplified by
those discussed above, is in itself, capable of ordinarily
producing good images. However, under certain circumstances, such
as high humidity the image produced tends to have variable density
and a mottled or blotchy appearance. It has been found that this
problem may be overcome by providing an applicator means 13 to
apply an insulating liquid to the surface of the blocking electrode
5 forming a pool at 14 which fills the gap between blocking
electrode 5 and injecting electrode 1 until blocking electrode 5
reaches dispersion. The gap-filling insulating liquid may be
applied by any convenient method, For example, the liquid may be
applied by spray or dropper to the blocking electrode surface or to
the injecting electrode surface at a location so as to fill the
space between the electrodes. Where the particle suspension is,
alternatively, coated onto the roller-blocking electrode instead of
the injecting electrode, the corona-preventing liquid may be
applied to the injecting electrode, either by moistening the entire
surface of the injecting electrode or by forming a pool at the gap
between the electrodes. It appears that this gap-filling insulating
liquid prevents corona discharge or air ionization between
electrodes 5 and 1 and thus eliminates disruption of the image.
Any suitable insulating liquid may be used as the carrier for the
photosensitive particles in this system. Typical carrier materials
are decane, dodecane, N-tetradecane, paraffin, beeswax or other
thermoplastic materials, Sohio Odorless Solvent 3440, (a kerosene
fraction available from Standard Oil Company of Ohio) and Isopar-G
(a long chain saturated aliphatic hydrocarbon available from Humble
Oil Company of New Jersey).
As discussed above, any suitable insulating liquid may be used to
fill the gap between the injecting and blocking electrodes. Good
quality images have been produced with voltages ranging from 300 to
5,000 volts, in the apparatus of the FIGURE.
The following examples further specifically define the present
invention with respect to the use of an insulating liquid between
the electrodes before imaging in an electrophoretic imaging system.
Parts and percentages are by weight unless otherwise indicated. The
examples below are intended to illustrate various preferred
embodiments of the present invention.
All of the following examples are carried out in an apparatus of
the general type illustrated in the FIGURE with the particle mix 4
coated on a NESA glass substrate through which exposure is made.
The NESA glass is connected in series with a switch, a potential
source, and the conductive center of a roller having a coating of
Baryta paper on its surface. The roller is approximately 21/2inches
in diameter and is moved across the plate surface at about 1.45
centimeters per second. The plate employed is roughly 3 inches
square and is exposed to a light intensity of about 8,000 foot
candles as measured on the uncoated NESA glass surface. The
suspension is exposed to an image by means of a conventional
transparency. Examples I--V use a black-and-white transparency and
produce monochromatic images. Examples VI--X use a "Kodachrome"
transparency and produce full color images. All pigments which have
a relatively large particle size as received commercially or as
made are ground in a ball mill for 48 hours to reduce their size to
provide a more stable dispersion which improves the resolution of
the final images.
EXAMPLE I
About 8 parts of 2, 4, 6-tris(3'-pyrenylazo) phloroglucinol is
mixed with about 100 parts Sohio Odorless Solvent 3440. This
dispersion is coated onto the NESA glass substrate. No liquid is
introduced into the gap between the roller electrode and the NESA
glass substrate; leaving a small air gap therebetween. Relative
humidity is measured and is found to be about 35 percent. A
potential of about 2500 volts is imposed on the roller electrode
during exposure. After exposure, an image corresponding to the
original is seen on the NESA surface and a negative image is seen
on the Baryta surface of the roller electrode. The positive image
is of excellent quality but with slight variations in density
across the image surface.
EXAMPLE II
The imaging process of Example I is repeated, except that
sufficient Sohio Odorless Solvent 3440 is applied to the roller
electrode before imaging to fill the air gap between the roller
electrode and the NESA glass substrate before the potential is
applied between the electrodes. After exposure, an excellent image
corresponding to the original is observed on the NESA surface.
Resolution and contrast are equal to that produced in Example I and
image density is somewhat more uniform across the image
surface.
EXAMPLE III
The imaging process of Example I is repeated, however, the relative
humidity is maintained at about 85 percent. An image of good
quality but with severe variations in density and a mottled and
blotchy appearance results.
EXAMPLE IV
The imaging process of Example III is repeated, except that
sufficient Sohio Odorless Solvent 3440 is applied to the surface so
as to fill the air gap between the roller electrode and the NESA
surface before potential is applied across said electrodes. The
image produced is of excellent quality with much improved image
density uniformity.
EXAMPLE V
The imaging process of Example IV is repeated, except Isopar-G is
applied to the blocking electrode surface instead of the Sohio
Odorless Solvent 3440. The image produced is of excellent quality
with very uniform density across the image surface.
EXAMPLE VI
A pigment mix is prepared comprising equal parts of a yellow
pigment, Algol Yellow GC, 1, 2, 5, 6-di(C,
C'-diphenyl)-pyrazol-anthraquinone, C.I. No. 67300, available from
General Dyestuffs; a magneta pigmnet, Locarno Red X-1686,
1-(4'-methyl-5'-phyloroazobenzene-2'-sulfonic
acid)-2-hydroxy-3-naphthoic acid, C.I. No. 15865, available from
American Cyanamid; cyan pigment, a cyan pigment, Monolite Fast Blue
GS, a mixture of alpha and beta forms of metal-free phthalocyanine,
available from Arnold Hoffman Company. About 8 parts of this
mixture is dispersed in about 100 parts Isopar-G and the suspension
is coated onto the NESA glass substrate. No liquid is applied to
the roller electrode surface, leaving an air gap between the roller
electrode and the NESA glass substrate. Ambient relative humidity
is about 40 percent. A potential of about 2500 volts is imposed on
the roller electrode during exposure. After exposure, a full color
image corresponding to the original is seen on the NESA surface.
This image is of excellent quality, however, there is a noticeable
variation in image density across the image surface.
EXAMPLE VII
The imaging process of Example VI is repeated, except that
sufficient Sohio Odorless Solvent 3440 is applied to the roller
electrode surface so as to fill the gap between the roller
electrode and the NESA glass substrate before potential is applied
across the electrodes. Again, the image produced is of excellent
quality. Here, however, image density is uniform across the image
surface.
EXAMPLE VIII
The imaging process of Example VI is repeated, except that ambient
relative humidity is maintained at about 85 percent. The image
produced is of satisfactory quality; but with severe variations in
image density across the image surface, giving a blotchy or mottled
appearance to the image.
EXAMPLE IX
The imaging process of Example VIII is repeated, except that
sufficient Sohio Odorless Solvent 3440 is applied to the roller
electrode surface so as to fill the air gap between the roller
electrode and the NESA glass substrate before a potential is
applied across the electrodes. The image produced is of excellent
quality with very little variation in image density across the
image surface.
EXAMPLE X
The imaging process of example IX is repeated, except that the
liquid applied to the roller electrode surface to fill the air gap
is decane, instead of Sohio Odorless Solvent 3440. Again, an
excellent image is produced with little variation of density across
the image surface.
Although specific components and proportions have been described in
the above examples, relating to electrophoretic imaging, other
suitable materials, as listed above, may be used with similar
results. In addition, other materials may be added to the gap
filling insulating liquid or to the particle suspension to
synergize, enhance, or otherwise modify their properties. For
example, the particle dispersions may be dye sensitized or
electrically sensitized, if desired, or may be mixed or otherwise
combined with other photosensitive materials, both organic and
inorganic.
Other modifications and ramifications of the present invention will
occur to those skilled in the art upon a reading of the present
disclosure. These are intended to be included within the scope of
this invention.
* * * * *