Note: Descriptions are shown in the official language in which they were submitted.
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B~CKGROUND OF T~IE INVENTION
The present invention relates to improvements
in high speed image reproduction. More particularly, the
invention is concerned wi-th an improved method and .system
for reproducing an image by the electro-coagulation of
an electrolytically coagulable colloid.
Applicant has already described in his U.S.
Patent ~o. 3,892,645 of July 1, 1975 an electric printing
method and system in which a thin layer of a liquid
composition contalning a colloid such as gelatin or
albumin, water and an electrolyte is interposed between
at least one pair of opposite negative and positive
electrodes spaced from one another to define a gap which
is filled by the liquid cornposition. In one embodiment,
there is a plurality of electrically-insulated juxtaposed
negative electrodes and selected ones thereof are elec-
trically energized to pass electric pulses throu~h the
layer at selected points to cause point by point
selective coagulation and adherence of the colloid on
the positive electrode directly opposite each energized
negative electrode, thereby forming imprints.
It is very important that the gap between the
negative and positive electrodes be uniform throughout
the active surfaces of the electrodes since otherwise
there will be a variation in the thickness of the layer
and thus a corresponding variation of the electrical
resistance thereof at different locations between the
electrodes, which will result in a non-uniform image
reproduction as the thic]~ness of the coagulated colloid
ls proportional to the amount of current passed through
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the layer. Since this gap is of the order of 50 ~, its
uniformity is of course very difficult to controlO More-
over, where the negative electrode~ are energized more
than once in the reproduction of an image, these become
polarized resulting in a gas generation and accumulation
at the negative electrodes, which adversely affect the
image reproduction.
SUMMARY OF THE INVENTION
_
It is therefore an object of the present inven-
tion to overcome the aforementioned drawbacks and toprovide a method and system for reproducing an image by
the electro-coagulation of a colloid, which do not
necessitate a critical control of the electrode gap nor
cause electrode polarization which may hinder the image
reproduction.
According to one aspect of the i.nvention,
there is provided a method of reproducing an image by
electro-coagulation of an electrolytically coagulable
colloid, which comprises the steps of:
a~ providing a plurality of negative and
positive electrolytically inert electrodes electrically
insulated from one another and arranged to define a
matrix of dot-fonming elements, the negative and positive
electrodes of each matrix element having respective planar
active surfaces with the negative electrode active surface
extending in the same plane as the positive electrode active
surface and in close proximity thereto,
b) applying a layer of a substantially liquid
colloidal dispersion over the negative and positive electrode
active surfaces of the matrix elements whereby the negative
and positive elec-trode active surfaces are disposed on the
same side of the layer of colloidal dispersion, the colloidal
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dispersion containing an electrolytically coagu]able colloid,
a liquid dispersing medium and a soluble electxolyte and hav-
ing a substantially uniform temperature throughout the layer
c) generating an electrical field between the
negative and positive electrodes of selected ones oE the
matrix elements, the electrical field extenaing substantially
parallel to the planar active surfaces of the negative and
positive electrodes, whereby to cause selective coagulation.
and adherence of the colloid onto the positive electrode
active surfaces of the selected matrix elernents, thereby
forming a series of corresponding dots representative of a
desired image, and
d) removing any remaining non-coagulated colloid.
The invention also provides, in a further aspect
thereof, a system for reproducing an image by electro-
coagulation of an electrolytically coagulable colloid, which
comprises:
- a plurality of negative and positive electroly-
tically inert electrodes electrically insulated from one
another and arranged to define a matrix of dot-forming elements,
the negative and positive electrodes of each matrix element
having respective planar active surfaces with the negative
electrode active surface extending in the same plane as the
positive electrode active surface and in close proximity there-
to, the electrode active surfaces being adapted to receive
thereover a layer of a substantially li~uid colloidal dis-
persion containing an electrolytically coagulable colloid, a
liquid dispersing medium and a soluble electrolyte and having
a substantially uniform temperature throughout the layer, and
- means for electrically energi.zing the negative
and positive electrodes of selected ones of the matrix elements
to cause selective coagulation and adherence of the colloid
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onto the pos.itive electrode active surfaces of the selected
matrix elements and to -thereby form a series of corresponding
dots representative of a desired image.
Thus, according to the invention, since the active
surfaces of the negative and positive electrodes are no longer
disposed opposite one another in differen-t planes, but rather
extend in substantially the same plane, there is no longer any
necessity of having to control in precise manner the thickness
of the layer of colloidal dispersion applied. Also, since the
electrodes of each dot-forming rnatrix element are eneryized
only once in the reproduction of an i.mage, there are barely
any electrode polarization and resulting gas accumulation that
may hinder -the image reproduction.
In a preferred embodiment of the invention, the
negative and positive electrodes of the matrix comprise
respectively first and second sets of mutually electrically-
insulated band-like electrode members disposed in parallel
side-by-side relation, the negative electrode members of the
first set extending transversely of the positive electrode
members of -the second set and being formed with a plurality of
protruding conductive elements which are spaced along the
length thereof and each have a planar active end surface. The
protruding elements of each negative electrode member extend
through corresponding bores formed in the positive electrode
members to te.rminate flush therewith such that the planar
active end surface of each protruding element and a planar
active surface portion of each positive electrode member
adjacent each bore extend in a substantially common plane
whe-reby to define the aforesaid matrix elements. Thus, the
electrical energizing of the negative and positive elec-trodes
of selected ~atr:ix elements may be effected by se~uentially
energizing the electrode members of one set and concurrently
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energizing selected ones of the electrode members of
the other set. Preferably, the positi~e electrode
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members are sequentially energized while selected ones of
the negative electrode members are concurrently energized.
rrhe concurrent selective energizing of the
electrode members of the other set is advantageously
effected by sweeping such electrode members and trans-
mitting electrical pulses to selected ones thereof during
sweeping. These elec-trical pulses can be varied either
in voltage or time from one electrode member to another
so as to correspondingly vary the amount of coagulated
co~loid adhered onto the positive electrode active
surfaces of the selected matrix elements. This enables
one to form dots of varying intensities and thus to
reproduce the half-tones of an image.
The colloid generally used is a linear colloid
of high molecular weight, that is, one having a molecular
weight comprised between about 10,000 and about 1,000,000,
preferably ~etween 100,000 and 500,000. Examples of
suitable colloids include animal proteins such as
albumin, gelatin and casein, vegetable proteins such
as agar and synthetic copolymers such as polyacrylic
acid, polyacrylamide, polyvinyl alcohol and derivatives
thereof. ~ater is preferably used as the medium for
dispersing the colloid to provide the desired colloidal
dispersion.
The colloidal dispersion also contains a
soluble electrolyte which enables the water to have a
greater conductivity; the water is believed to migrate
under direct current towards the negative electrode and
thereby cause the colloidal dispersion to dry out, result-
3U ing in coagulation of the colloid and adherence thereo~
onto the positive electrode. Examples of suitable
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electrolytes include chlorides and sulfates, such as
potassium chloride, sodium chloride, calcium chloride,
nickel chloride, lithium chloride, ammonium chloride, and
manganese sulfate. Since the speed of electro coagulation
is affected by ternperature, the layer of colloidal dis-
persion must be maintained at a substantially constant
temperature, for instance by using a thermostatic water
jacket, in order to ensure a uniform image reproduction.
After coagulation of the colloid, any remaining
non-coagulated colloid is removed by any suitable means,
such as by washlng off, airjet or wiping to fully uncover
the coagulated colloid.
The applications of the invention are basically
the same as those mentioned in Applicant's U.S~ Patent
15 ~o. 3,892,645. For example, the coagulated colloid can
~e colored with a water-soluble dve which is absorbed
thereby and the colored coagulated colloid may then be
transferred onto an end-use support, such as paper.
The coagulated colloid can also be set or hardened
chemically or by irradiation so as to be used for off-
set lithographic printing. Moreover, it is possible to
produce several differently colored images of coagulated
colloid which can be transferred onto an end-use support
in superimposed relation to provide a polychromatic
ima~e.
~RIEF DESCRIPTION OF THE DRAWI~GS
Further features and advantages of the inven-
tion will become more readily apparent from the following
description of preferred embodiments thereof as illus-
trated by way of e~amples in the accompanying drawings,
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in which:
Figure 1 schematically illustrates an image
reproduction system according to the inven-tion, the dot
rnatrix printer of which is shown partially cut away,
Figure 2 is fragmentary exploded view of the
dot matrix printer shown in Fig. 1,
Figure 3 is a sectional view taken along line
3-3 of Fig. l;
Figure ~ is another sectional view taken along
line 4-4 of Fig. 1,
Figure 5 is a top view of a matrix element of
the dot matrix printer shown in Fig. 1, and
Figure 6 is a view similar to Fig. 5 but show-
ing a different type of matrix element.
The image repro~uction system illustrated in
Fig. 1 includes a dot matrix printer which is generally
designated by reference numeral 10 and comprises two
superimposed sets of electrically-insulated negative and
positive band-like electrode members 12 and 14 disposed
in parallel side-by-side relation, the negative electrode
members 12 extending transversely of the positive
electrode members 14 to define at their intersections a
plurality of dot-forming matrix elements 16. Each
negative electrode member 12 is electrically connected
to a sweepirlg device 18 which is connected to the
negative terminal of a direct current power supply ~0
via a modulator 22 coupled to an electronic counter 24
operative to transmit electrical pulses to selected ones
of the electrode members 1~ during the sweeping thereof
by the device 180 The modulator serves to vary
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the electrical pulses either in voltage or time.
Each positive electrode member 14, on the other
hand, is electrically connected to another sweeping
device 1~' which is connected to the positive terminal
of the power supply 20. Thus, the electrodes of
selected ones of the matrix elements 16 are electrically
energi~ed by sequentially energizing the positive
electrode members 14 with the sweeping device 18' and
concurrently sweeping the negative electrode members
12 with the device 1~ while transmitting with the counter
24 electrical pulses to selected electrode members 12,
which are modulated either in voltage or time by the
modulator 22.
As shown in Figs 2-4 t the negative and positive
electrode members are electricall~ insulated from one an-
other by means of a layer of insulating material 26 having
a thickness of about 10 ~. The negative electrode mem-
bers 12 are also electrically insulated from one another
by a layer of insulating material 28 having a thickness
of about 25 ~. The positive electrode members 14 are
similarly insulated by means of a layer of insulating
material 30 having a thickness of about 10 to 25 ~,
preferably 10 ~. Each negative electrode member 12 is
formed with a plurality of protruding conductive elements
32 of circular cross-section which are spaced along the
length thereof and each have a planar active end surface
34. The protruding elements 32 of each negative electrode
12 extend through corresponding bores 36 formed in the
positive electrode members 14 to terminate flush there-
with such that the planar active end surface 34 of eachelement 32 and a planar active surface portion 3~3 of a
positive electrode member 14 adjacent a bore 36 extend
in a comrnon plane. Each protruding element 32 is of
course electrically insulated from its adjacent positive
elec-trode member 14 by means of a layer of insulating
material 40 swch as silicon mono~ide, having a thickness
of about 5 to 10 ~, preferably 10 ~.
Thus, the planar end surface 34 of each protrud-
iny element 32 and the planar surface portion 38 of each
positive electrode member 14 adjacent each element 32
constitute the electrode active surfaces of each dot-
forming matrix element 16. Each matrix element prefer-
ably has a square surface area of abou-t 125 ~ x 125 ~,
the protruding element 32 of each matrix element 16
being disposed cen-trally thereof and having a diameter
of about 25 to 50 ~, the elements 32 are therefore
invisible to the naked eye. The dot matrix printer 10
comprises about 40,000 of such ma-trix elements 16 per
square inch.
The negative electrode members 12 can be made
of any metal, copper or stainless steel being preferred.
However, the positive electrode members 14 must be made
of a metal that will resist electrolytic attack and
enhance electro-coagulation, such as stainless steel,
aluminum, nickel, chromium or tin, these metals being
2~ electro-negative with respect to hydrogen. The surfaces 3
of the positive electrode members 14 are advantageously
unpolished to enhance the adherence of the coagulated
colloid thereon. The electrode members 14 can be produced
by ion sputtering and can thus be as thin as 10 ,u~
In order to reproduce an image with the
system ~ust described, a layer of a liquid colloidal
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dispersion containing a colloid such as ge:Latin or
albumin, water and an electrolyte such as potassium
chloride, and having a suhstantially uniform temperature
throughout -the layer, is applied over the surface of the
dot matrix printer 10. The sweeping devices 18 and 18'
and the counter 24 are then activated so as to elec-
trically energize the electrodes of selected ones of the
matrix elements 16 and thereby cause selective coagula-
tion and adherence of the colloid onto the positive
electrode active surfaces 38 of the selected matrix
elements, the coagulated colloid 42 ~orming a series
of corresponding dots representative of the desired
image.
The layers of insulating material 30 between
the positive electrode members 14 should be as thin as
possible so as to provide a continuous image and not
one which is streaked. The layer of insulating material
40 surrounding each protruding element 32 should also
be as thin as possible since the thinner the la~er 40
the faster is the speed of electro-coagulation.
Instead of having matrix elements 16 each
formed with a single centrally disposed protruding
element 32 as shown in Fig. 5, ;t is of course also
posslble to provide matrix elements 16' each formed with
a plurality of spaced-apart elements 32 as represented
in the embodiment illustrated in Fig. 6. Such an arrange-
ment enables one to produce an image having a more
uniform tone repartition.
With the image reproduction system described
above, it has been observed that the power required to
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produce coagulation over a square surface area of about
125 ,u x 125 ~ is the charge of an electrolytic capacitor
of 2 micro farads at 50 volts. In o-ther words, using a
power generator of 25 wat-ts (50 V, 500 mA), one can
produce about 100,000 dots per second.
Although the dot matrix prlnter 10 has been
illustrated as having a planar display surface, it is
apparent that the whole surfaces of the positive
electrode members 14 which constitute the display surface
of the printer 10 need not be planar, provided however
that the electrode active surfaces of each matrix element
be planar and extend in a substantially common plane.
Thus, for example, a cylindrical dot matrix printer could
be designed in which each matrix element would have the
required characteristic just mentioned.
