Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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FIEL~ OF THE INVENTION
This invention relates to printing and, more
particularly, to a method of making a printing plate by
electrolytic coagulation and printing ordinary paper with the
printing plate.
DESCRI TION OF PRIOR ART
In applicant s United States patent number 3,892,645
dated July 1, 1975 and entitled: "PRINTING METHOD AND SYSTEM BY
GELATIN COAGULATION, there is definecl a method for recording an
image including coagulation of a colloid composition. Electric
direct current is passed at desired places through a thin layer
of a liquid-state colloid composition containing an electrolyte,
by means of several negative electrodes and a single positive
electrolytically-inert electrode in contact with the layer, thus
achieving coagulation and adherence of part of the colloid to the
positive electrode and removing the non-coagulated colloid
composition to leave only the coagulated image.
It has been found that the patented me-thod may suffer
adverse secondary effects and speed restrictlons, making it less
suitable for more-demanding applications and for achieving
sustained reliable performance, such as for computer printers and
photocopying. Also, the colloids used in the patented method
make it impossible to print on ordinary paper, since it required
gelatinized paper, which is expensive. More specifically, it has
been found that the albumin or gelatin used in the above-noted
patent is not usually of consistent quality due to the high
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variance of its molecular weight and its different chemical pre-
treatment, as well as its ability to be adversel~ affected by
bacterial decornposition in ambient air.
OBJECTS OF THE INVENTION
_ _ _
It is the general object of the invention to obviate
the above-noted disadvantages.
It is another object of the present inventon to provide
a method of recording an image by electric coagulation, thus
forming a printing plate, and printing ordinary paper therewith,
the method achieving an increased printing speed and increased
reliability suitable for computer printing and photocopying.
DE CRIPTIO OF I~E PRE,FE.RRED EMBODIMENTS
As in the above-noted U.S. patent, the present
invention includes a method of recording an image comprising the
steps of interposing a thin layer in substantially-liquid state
contalning water, an electrolyte arld an electrolytically-
coabulable colloid between and in contact with a plurality of
negative electrodes, and A single posi~ive electrode, the
positive electrode being electrolytically inert, successively and
selectively biasing said electrodes with direct current for a
short period of time and concurrently sweeping the positive
electrode by the negative electrodes to thereby cause point-by-
point selective coagulation and adherence of the colloid onto
said positive electrode and removing the non-coagulated colloid,
whereby the coagulated colloid is representative of a desired
image. The improved method is characterized by the use of a
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colloid selected from the group consisting of water-dispersable
synthetic linear colloid polymers, of a molecular weight between
lO0,000 and 600,000 and, preferably, between 200,000 and 450,000
and including polyacrylic acid and polyacrylamide resins. The
uniform characteristics of the synthetic colloids, with a well-
controlled molecular weight, have been found to provide reliably-
uniform and superior results over the albumin and gelatin used in
the above-noted U.S. patent. The electrolyte used in the
composition is either an acid or a salt selected from the group
consisting of lithium, sodium, potassium and ammonium chloride.
The composition also preferably includes an electrode
depolarizing agent to minimi~e the deposition of gas against the
electrodes. Such an agent is preferably selected from the group
of manganese and nitrate compounds and H~02, which combines with
the gas producecl against the electrodes upon breakdown of a water
molecule into oxygen and hydrogen ions. Lead nitrate, rnanganese
chloride and H22 have been found suitable as a depolarlzing
agent. The positive electrode must be electrolytically inert.
Metals suitable for rnaking the positive electrode are selected
from stainless steel, aluminum and tin, with stainless steel
grade 316 being preferred as giving the best results. The non-
coagulated colloid composition is removed by washing or scraping
the positive electrode with a soft rubber squeegee. The anode
with the coagulated synthetic dots adhering thereto form the
printing plate. A water solution of a dye and of a swelling
agent for the coagulated dots of the printing plate is then
, . .
applied to the printing plate and the coagulated dots become
swollen as they absorb the solvent and absorb the dye. After
removing the surplus, of the dyed solution, the swelled, dyed,
coagulated image is pressed in close contact with ordinary paper
previously slightly wetted with an alcohol. Since the swelling
agent is soluble in the alcohol, the dye of~ the dots is
transferred onto the paper surface. Any ordinary paper can thus
be printed, including uncoated paper, such as bond paper and
coated paper, more specifically kaolin-coated and synthetic
resin-coated paper. The preferred swelling agent is a water
solution of a compound selected from the group consisting of one
or more of glycerol, ethylene glycol and sorbitol. These
compounds are soluble in the alcohol used as a paper wetting
agent and swells the coagulated dots much longer and much more
than just water. Thus, dye transfer from the printing plate to
the paper is highly efficient, fast and acc~lrate.
Preferred alcohols for paper wetting are selected from
the group consisting of methanol, ethanol and isopropyl alcohol.
These alcohols possess high paper wetting property and,
therefore, the colored glycerol, ethylene glycol or sorbitol, or
mixtures thereof, are absorbed by the paper fibers where they
remain. The d~e transfer on paper just described cannot work
with the gelatin and albumin colloids mentioned in the above-
noted U.S. patent. Sorbitol and ethylene glycol have only a very
slight swelling effect on gelatin or albumin and are totally
unsatisfactory for the above-described printing step.
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Gelatinized paper must be used to effect printing from the
printing plate where the coagulated dots are gelatin or albumin.
EXAMPLE 1
The following electrolytically-coagulable colloid
composition was prepared:
PERCENT BY WEIGHT
. . .
Polyacrylic acid
(Carbopol 907, a registered
trademark of B.F. Goodrich)
10 [molecular weight 450,000]: 10 grams 8.77
KCl electrolyte 4 grams 3.51
water lOO ~rams 87.72
total 114 grams 100.00
This water solution has a pH of 2.25. This solution
was used as a layer between the negative and positive electrodes
in the above-described method for recording an image. The
positive electrode was stalnless steel grade 316. The gap
between the negative and positive electrodes was 50 microns. The
neyative electrodes were copper-insulatad wires of 250 microns in
diameter arranged in a linear array. The electrodes were
successively biased by successively and selectively applying to
the negative electrodes a power supply of 25 watts (50 volts and
500 milliamperes). The operating temperature was 30 C. A speed
of coagulation of 300,000 dots per second was achieved, with the
size of the dots being 250 microns in diameter. This means that
an electric pulse at each electrode of one-three hundred
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thousandths of a second was necessar~ to effect coagulation.
The experiment was repeated several times and the
coagulation results were very constant ~rom one experiment to the
other. Additional experiments were repeated using the same
liquid composition but using negative elec-trodes having a
diameter of 125 microns instead of 250 microns. The resulting
speed of coagulation was found to be 1,000,000 dots per second,
that is requiring an electrical pulse for each negative elec~rode
of one millionth of a second.
Comparative experiments were made using the same set-up
but with gelatin and albumin as the colloid. The coagulation was
very inconsistent from one experiment to the other, and the speed
of coagulation using 250 microns negative electrodes was only
100,000 dots per second.
EXAMPLE II
A series of experiments were conducted for recording an
image using the same electrolytically-coagulable colloid
composition, but with the polyacrylic acid mentioned in Example I
replaced by a polyacrylic acid of molecular weight of 250,000 as
supplied by Aldrich under code number 18128-5, with the resulting
solution having a pH adjusted to 2.30. Very similar results were
obtained: other experiments were carried out and with similar
results using the following colloid polymer:
Polyacrylamide of molecular weight 200,000, supplied by Aldrich
under code number 19-092-6, with the solution a~justed to a pH of
~.46.
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Additional experiments were carried out with the same
results, using a copolymer of polyacrylamide and of polyacrylic
acid of molecular weight 250,000, as supplied by Cyanamid under
the registered trademark ACCOSTRENGTH 86, with the solution
adjusted to pH 4.63.
EXAMPLE_III
Experiments similar to those of the prior-mentioned
examples were carried out, but while varying the voltage applied
to the electrodes; it was found that the size or thickness of
the coagulated dots varied in proportion to the applied voltage,
thus permitting the reproduction of half-tones.
EXAMPLE IV
To the liquid electrolytically-coagulable colloid
composition of any of the above noted examples, was added a
depolarizing agent consisting of two percent by weight of a
compound selected from lead nitrate, manganese chloride and H2O2,
with even better results.
_AMPLE. V
The coagulated synthetic resin dots of the printing
plate obtained from any of the foregoing examples were swollen
and colored by applying thereto the following solution:
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PERCENT BY WEIGHT
water soluble dye selected from Pina dyes
and obtained from RIDEL-deHAEN ~West Germany~,
namely:
pina yellow N 28,5995 grams 3.84
glycerol 20 c.c. or25.2 grams 19.35
water _ _00 qrams _76.~1
total 130.2 grams lO0.00
The coagulated dots became quickly and highly swollen
and absorbed the dye. The surplus dye solution was then removed
and the swelled, dyed coagulated image was pressed in close
contact with a kaolin-coated paper previously wetted with
methanol. The methano]., which is a solvent ~or glycerol, caused
the transfer ~f the dye to the paper surface, resulting in the
image transfer to the paper. About seven paper sheets were thus
printed with the same printing plate, while recharging the
synthetic dots with the dye and swelling agent each time; it was
found that up to about seven sheets could be printed. To print
additional sheets, it was necessary to remake the printing plate.
Each time a paper sheet was printed, there was not only
a dye transfer but also a transfer of a portion of the coagulated
dots. Very precise and clear images were obtained on the paper
sheets.
EX~MP E VI
The same experiments were carried out as in Example V,
but while using the following coloring and swelling composition:
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PERCENTAGE BY WEIGH.T
pina blue N 28,597 5 grams 3.61
ethylene glycol 30 c.c. 33.46 grams 24.17
or
water _ 100 arams __72.22
total 138.46 grams 100.00
The paper wetting agent was ethanol and similar results
as in Example V were obtained.
EXAMPLE VII
10 The same experiments as Example V were carried out but
using the following coloring and swelling agent composition for
treating the coagulated dots of the printing plate image:
_R ENT_ Y WEIGHT
pina violet N 28,5985 grams 3.23
15 sorbitol 50 grams 32.25
water _ 00 cirams 64.52
total 155 cJrams 100.00
Isopropyl alcohol was used as the paper wetting agent.
The dye transfer to the paper was less than in Examples V and VI,
since sorbitol is a poorer solvent and, therefore, a poorer
swelling agent than glycerol or ethylene glycol for the
coagulated dots of the colloids named in Examples I to IV.
However, it was found that, when sorbitol is admixed with either
or both glycerol and ethylene glycol, the coagulated colloid
swelling ef~iciency can be adjusted for maximum dye transfer to
the paper.
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EXAMP E VIII
The same experiments as in Examples V to VII were
carried out~ but the printing step was carried out on bond paper.
This necessitated heating the printed sheet by hot-blown air to
accelerate its drying, in order to prevent spreading of the dye
through the paper fibers.
EXAMPLE IX
Experiments were carried out in accordance with
Examples I, II and IV, while varying the voltage applied to the
electrodes, followed by paper printing in accordance with
Examples V to VIII, and the printed image exhibited the 64 grades
of half-tones as required for image printing in photographic work
EX~IPLE XI
The same experiments were carried out as in example V of
the principal disclosure, but while using the following
coloring and swelling composition:
PERCENT BY WEIGHT
water soluble dye: Pina blue No. 28,597 5%
N-methyl pyrrolidone 20%
water 75%
The paper wettin agent was acetone in one set of exper-
iments and isopropyl alcohol in the other set.
Dye transfer was even more accurate than in Example X
during printing.
EXAMPLE XII
The same experiments with the same results were carried
out as in Example IX of the principal disclosure but while
varying the duration of the applied vol-tage instead of
varying the vol-tage.
s.d.)
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SUPPLEMENTARY DISCLOSURE:
Since the filing of the present application a great
number of additional chemicals have been tested for carrying
out the different s-teps of applicant's method.
The following have been found: the principal disclosure
mentions that, as a swelling agent, glycerol, sorbitol and
ethylene glycol are suitable. It has now been found that
increased swelling can be achieved by the use of formamide or
N-methylpyrrolidone.
As a wetting agent, it has now been found that acetone
can be used to great advantage.
Finally, it has been found -that not only polyacrylic
acid and polyacrylamide resins can be used as the colloid
but also copolymers of these two substances.
Finally, it has been found that the si~e or thickness
of the coagulated dots may be varied not only by varying the
applied voltage, but also by controlling the duration of the
electric pulse applied to the colloid layer.
The following experiments were effected:
EXA~1PLE X
The same experiments were carried out as in Example V
of the principal disclosure but while using the following
coloring and swelling agent:
PERCENT BY WEIGHT
Pina blue No. 28,597 5
ethylene glycol 20~
formamide 20%
water 55%
The paper wetting agent was acetone instead of methanol. Dye
-transfer during printing was more accurate than in Example V.
-12- ~s.d.)
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