Note: Descriptions are shown in the official language in which they were submitted.
3'~7~1
Case 1481/1~5/1486
PRINTING METHOD AND APPARATUS
BACKGROUND OF THE INVENTION
This invention relates to printing systems using a
printing element on which the image is defined in terms of
contiguous hydrophilic and relatively hydrophobic regions,
and which is capable of serving as a printing plate or other
analogous source of a transferable ink image. More
specifically, this invention relates to a novel printing
system comprising a non-photosensitive, reusable printing
surface suitable for use in a lithographic-type or other
printing system, on which an ink image may be formed,
refreshed, or completely reconfigured electronically,
without a separate development or plate making step, without
removal of the printing element, and without substantial
interruption of the printing process.
In modern printing systems using printing plates such as
letter-press and intaglio or Grover systems, the image
portions of the printing plate are defined in terms of
raised or recessed areas of the plate surface which are made
to carry ink. In planographic systems such as lithography,
however, the image portions of the printing plate, i.e.
those portions of the printing plate surface intended to
carry ink, are formed at substantially the same surface
I aye
level as the rest of the plate. Rather than depend upon the
relative elevation of portions of the plate surface -to
define the ink-beariny image, planographic systems deperld
upon certain areas of the plate having a greater relative
affinity for water than is shown by the remaining areas o-F
the plate.
In a typical lithographic printing system, the relative
immiscibility of grease and water is used to define and
maintain the image and non-image areas of the printing
plate. In standard lithographic printing systems where
greasy-type or Leo inks are used, the lithographic plate is
made oleophilic (grease-loving) and hydrophobic
(water-hating) in image areas (i.e., those areas which will
receive and transfer ink to the paper sheet or other
material to be printed), and hydrophilic (water-loving) in
the non-image areas. These latter areas, which are in
image-complementarv configuration, are sometimes referred to
as "lithographically blank" areas, because they normally
carry or transfer no ink. So long as sufficient Atari is
present in these lithographically blank areas, no oleo-type
ink will adhere two the plate in these non image areas. my
this arrangement, these hydrophilic, image-complerentary
areas of the plate will retain preferentially an aqueous
fountain or dampening fluid applied to the plats? to the
exclusion of the remaining portions of the plate, and will
thereby allow the greasy ink applied thereafter to adhere
~27'D.~
only to the oleophilic areas of the plate intended Jo carry
the ink image.
Various techniques have been developed far establishing
the hvdrophilic and hydrophobic areas of the printing plate.
The most popular writhed of establishing such lmage-defining
areas is with the aid of light sensitive materials which
tend to undergo chemical reactions when exposed to actinic
light. In a typical process, when using negatlve-inlaged
films, the so-called "negative" plate is covered with a
layer of a light sensitive dyes or photo polymeric
formulation. Strong light energy passing through the
negative film and striking the plate causes the dyes or
photo polymeric formulation in the exposed or imaged areas of
the plate to undergo a chemical change, e.g., to polymerize,
forming whereby a hardened, hydrophobic, ink receptive area.
The non-polv~erized formulation in the unexposed or
image-complementary areas of the plate is removed by washing
the plate surface with a solution in which only the
unexposed, non-polymerized formulation is readily soluble.
These unexposed, washed areas are then treated with gum,
i.e., a gum formulation containing gum Arabic carboxymethyl
cellulose gum, or the like. Often, the non-polymerized
formulation is washed away and the gum added in a single
step. If a ions wearing plate is desired, a thin film of a
25 gum-containing material may be rubbed onto or otherwise
applied to the plate and the plate surface washed with
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water, thereby causing a water insoluble layer of gum to be
adsorbed onto the unexposed or image-complementary areas of
the plate surface, and forming a highly hydrophilic surface
which will wet readily with water, and will thereafter
reject ink.
If a positive rather than a negative type film is used,
the so-called "positive" plate is first sensitized with a
light sensitive coating which degrades when exposed to
actinic light. Exposure of the plate, via the positive
film, then results in degradation of the coating in what
will be the image-complementary (i.e., non-ink-carrying)
portions of the image. The coated plate is chemically
washed to remove the degraded areas of the coating. The
plate is then baked to harden the coating in the image
(i.e., ink-carrying) areas, and coated with a gum-containing
material such as gum Arabic or the like, as is done with the
"negative" plate discussed above.
Systems using light sensitive materials customarily
require the preparation of a photographically-generated film
negative or positive transparency, as well as the careful
projection of the image carried by the transparency onto the
light sensitive surface of the plate. In certain systems,
e.g., in so-called photo-direct systems, a plate may be
exposed directly by the original copy without the need for
an intermediate film transparency. In either case, however,
it is usually necessary that the resulting plate be
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developed and rinsed and a finishing solution usually must
be applied.
Electrostatic systems for generating a lithographic
plate may be based on use of either a hydrophilic or a
hydrophobic toner material. If, for example, a hydrophobic
toner material is used, a plate surface comprising a
photo conductive material which is hydrophilic is given a
uniform electrical charge prior to being exposed to light
striking the plate in image-complementary configuration.
The light causes neutralization of the electrical charge in
the illuminated areas of the plate. To develop the plate, a
toner carrying a charge opposite to that of -the remaining
charged areas of the plate is then applied and made to stick
to the plate surface. After fusing, the toned areas become
I hydrophobic, while the unzoned areas remain hydrophilic.
use of a hydrophilic toner material employs analogous
process steps with an initially hydrophobic plate surface.
The lithographic-type plates produced by the various
techniques discussed above, as used in printing presses and
processes of conventional design, generally exhibit
substantial deficiencies which are well known and commonly
encountered in the printing industry. Representative of
these deficiencies are the following:
1) inability to venerate a high quality
lithoyraphic-type printing plate without film preparation
steps or without elaborate plate exposure and development
procedures;
I
2) inability to reconfigure completely the image being
printed by the plate without substantial interruption of the
printing process or substitution of a second plate carrying
the desired reconfigured image;
3) inability to refresh or renew the oleophilic and
hydrophilic areas of the image carried by the printing plate
without substantial interruption of the printing process;
4) inability to correct minor deficiencies in the image
being printed by the plate - for example, those deficiencies
caused by incomplete or unintended removal of material from
the plate surface, or by foreign matter residing on the
plate surface - without substantial interruption of the
printing process;
5) inability to correct substantial registration errors
in the plate without replating;
6) inability to print a continuously repeating pattern
on a web substrate using a rotary-type press without a gap
or seam between plate image pattern repeats and without the
use of additional plates or ink heads;
7) inability to print a pattern wherein the repeat
length is greater than, or wherein the repeat length will
not integrally divide into the plate length or circumference
of the pi ate roll;
8) inability to eliminate roll shock, i.e., the
mechanical interaction between the respective gaps of the
plate and blanket roils in rotary offset printing methods,
which limits press speeds;
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9) inability to proof conveniently a freshly generated
plate under true production conditions, using production
inks, papers, etc.;
10) inability to s-tore the equivalent of a large
library of printing plates for short or periodic printing
runs without substantial maintenance and inventory costs;
11) inability to generate a lithographic-type printing
plate, which requires no separate developing process, or
print imagery using a lithographic-type printing process,
directly prom a source of electronically-generated images
such as a digital computer.
Attempts to overcome these and other deficiencies of
existing systems generally have met with only limited
success. Disclosed herein is a printing system employing a
reusable printing plate which overcomes all of the
above-listed deficiencies, as well as others associated with
almost all photo lithographic techniques, such as halation
(i.e., imperfect light exposure caused by the reflective
nature of the printing plate supporting base).
A substantially planographic plate suitable for service
in a lithographic-type printing system is described herein
which is comprised of an intrinsically hydrophilic plate
material which supports a thin hydrophobic layer thereon.
Also described herein is a method for generating, imaging,
and using such a plate to print electronically generated
images in various printing processes. According to the
~327g~
teachings herein, a method for generating a plate for use in
a lithographic-type printing system comprises coating
uniformly an intrinsically hydrophilic support surface with
a thin hydrophobic layer of a suitable material, then
selectively removing the material in a predetermined
configuration by means of an electronically addressable
imaging system utilizing an electric spark discharge, a beam
of electromagnetic energy (e.g., a laser beam), a beam of
ionized particles, or other means. Alternatively, the
hydrophilic plate surface may be first coated with a thin
layer of a hydrophilic protective material, for example, a
gum-containing material, prior to the application and
selective removal of the material forming the hydrophobic
layer. As additionally taught herein, suitable material for
forming a hydrophobic layer may be directly, selectively
applied to the plate in the desired configuration. Whether
selectively removed or selectively applied, the hydrophobic
layer material may be said to be arranged over the plate
surface in a desired image-related configuration. These as
well as other developments, all of which involve a reusable,
easily re-imageable ink image generation surface useful in
various printing processes, are described herein. As used
herein, ink image generation surface is intended to mean the
surface on which the ink image corresponding to the desired
printed image is initially formed. This surface generally
will be the surface on which a prank latent image, i.e.,
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an image defined in terms of adjacent hydrophilic and
hydrophobic ureas, is also initially formed. The term
"imaging" is intended in mean the generation of this latent
image, prior to the application of ink.
described herein is a surface suitable for use, for
example, as a planographic printing plate in either rotary
or non-rotary printing systems wherein an electronically
embodied image may be impressed directly onto the plate,
without requiring the use of photosensitive materials or
I coatings, or without elaborate developing steps. In
addition, the disclosed surface is reusable, in the sense
that a lithographic plate, for example, when imaged and used
for printing in accordance with the teachings of this
invention, may be reimaged with the same or with a totally
different image without the need for replacing the plate.
In fact, an image having a length greater than (or not an
integral divisor of) the circumference of the plate roll,
where such roll is used, may be printed by changing the
image associated with one portion of the plate roll while
I another portion of the roll is transferring an ink image to
an offset roll or directly to a substrate.
Throughout this discussion, the terms "printing plate"
or "plate" shall be used to describe a substantially flat,
planographic surface capable of recording on image defined
in terms of hydrophobic and relatively hydrophilic areas;
such a surface may be the ink transfer surface associated
~2~7~Q
with either a planar or curved lithographic printing plate,
and may even be, for example, the print roll surface itself
and not a separate, detachable entity usually associated
with the term "plate." The printing plate may take the form
of a planar surface, a cylinder, an endless belt, or other
form. I-t is foreseen that the printing element as described
herein may also comprise the printed product, e.g., the
plate need not serve as an ink transfer surface, but as the
printed substrate itself. In addition, other,
non-planographic surfaces may be employed as well.
A method and apparatus is herein disclosed which can
completely eliminate the costs associated with generating a
plate using conventional photo lithographic techniques, as
well as the cysts involved in maintaining a conventional
plate library for short-run or periodic printing jobs. The
necessity of replacing a plate when a sharpened, or slightly
modified, or totally reconfigured image is desired is
completely eliminated. The costs and limitations associated
with having gaps in the plate used in rotary-type presses
which cause a printing gap or seam in matter printed on long
webs, as well as the mechanical shock associated with such
plate gaps and the speed limitations such plate gaps impose,
can be completely eliminated by imaging the roll surface as
herein described, rather than imaging a separately attached
printing plate of conventional design. Additionally, a
series of pre-productlon run proofs may be generated
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inexpensively, and with the advantage that the proofs may be
printed on the same machine, using the same plate, paper,
inks, and many of the same press adjustments as the final
production run, thereby eliminating any doubt whatsoever as
to the appearance of the final printed image. lJhatever
adjustments are necessary to develop a satisfactory proof,
regardless of their magnitude, can be made to the plate
without removing the plats from the press, or having in make
ready and install an entirely new plate.
The teachings herein may be used in a wide variety of
printing applications, particularly where, for example,
minimal costs for plate preparation, set up, storage, or
inventory are desired, or where no gap or seam between plate
images on a continuous printed substrate is desired.
because of the lack of any plate gap or seam and any
corresponding mechanical shock originating therefrom, the
teachings herein are also particularly suited to
applications wherein high speed printing (e.g., high speed
rotogravure speeds) is desired.
Other features and advantages will become apparent from
the following detailed description in which reference is
made to the Figures summarized below.
DESCRIPTION OF DRAWINGS
Figure l schematically depicts a rotary printing system
using printing plate described herein is being continuously
erased and reimaged by means of an electric spark discharge
-- I]
2 3 2
means while the plate is transferring a portion of the image
onto a web substrate;
Figure 2 schematically depicts the printing system of
Figure l wherein the plate is not being erased and
reimaged, but is being used to make a series of impressions
or copies on a web substrate of the existing image on the
plate;
Figure 3 schematically depicts an apparatus which may be
used to image a plate in accordance with the teachings
herein;
Figure 4 schematically depicts a printing system similar
to Figure l in which a laser has been substituted for the
electric spark discharge means;
Figure 5 schematically depicts a plate, attached to a
plate roll, embodying the teachings herein, as well as a
mask which may be used in imaging the plate;
Figure 6 schematically depicts a stylus bar, comprised
of individually addressable styli, of a type suitable for
imaging printing plates herein described according to the
teachings herein;
Figure 7 schematically depicts a rotary
lithographic-type printing system employing a control system
for correctly sequencing and controlling a variety of
operations directed to imaging, reimaging, or printing an
image on a substrate according to the teachings herein.
~3;~7~)
Figure 8 schematically depicts the system of Figure 7
which has been modified to include a separate hydrophilic
layer applicator;
Figure 9 schematically depicts a printing apparatus in
which a reusable cylindrical printing screen is used.
Figure 10 schematically depicts a magnified perspective
cross-section of an imaged planographic plate surface.
Figure 11 schematically depicts a magnified perspective
cross-section view of a portion of a Grover roll surface
which has been imaged according to the teachings herein.
Figure 12 schematically depicts a magnified perspective
cross-section view of a printing screen which has been
imaged according to the teachings herein.
DESCRIPTION OF PREFERRED EMBODIMENTS
In the apparatus and process depicted in Figure 1, a
plate roll or cylinder 10 is continuously reimaged with the
same or a different image or pattern at the same time a
substrate is being printed. As suggested above, the plate
may take a form other than a roll or cylinder. For example,
the apparatus of Figure 1 could be modified to accommodate
an endless belt having a suitable hydrophilic surface,
rather than the roll shown.
The process depicted in Figure 1, which may be a
lithographic process in which an Leo ink is employed, will
be explained beginning with cleaning roll stack lo. Stack
12 applies a conventional cleaning solvent to the surface of
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roll 10 which, in conjunction with soft doctor blade 14 and
solvent drying jets 15, removes at! traces of ink, fountain
solution, solvent, and foreign matter. without marring the
roll surface. If removal of any previously applied
hydrophobic layer material is necessary, it may be removed
with heat, solvents, or, perhaps most simply, by activating
the imaging means to produce a totally "blank" or
hydrophilic plate, as will be discussed later. similar
procedures may be employed if removal of gum is desired, as
will be discussed later.
The roll surface of plate roll 10 is comprised of a
material which is intrinsically substantially hydrophilic -
a material having a surface which, when clean, i.e., free of
significant contamination, is substantially hydrophilic.
Any suitable intrinsically substantially hydrophilic
material may he used in the present invention. Typical
suitable hydrophilic materials include, but are not
necessarily limited to, metals such as nickel, copper, tin,
aluminum, stainless steel, zinc, brass, phosphor bronze,
titanium, zirconium, palladium, niobium, platinum, lead,
molybdenum, tantalum, tungsten, iron, and gold, as well as
non-metallic materials such as an aluminum oxide/titanium
dioxide composite (60% Aye, 40% Tony and mixtures
thereof. While any suitable intrinsically hydrophilic
material may be used with this invention, stainless steel
and aluminum are particularly suitable for many
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applications. If, under some circumstances, the roll
material chosen tends to form a relatively hydrophobic
coating (e.g., a coating of airborne contaminants, etc.)
upon exposure to the atmosphere, it may be desirable to coat
the roll surface with a layer of a suitable protective
material, for example, a gum formulation containing gum
Arabic carboxymethyl cellulose gum, or the like, which
formulation will herein be referred to simply as "gum."
Such coating I also recommended if maximum longevity of the
image or the roll is desired. If done immediately following
the imagine process, the gum is attracted to the exposed
hydrophilic areas and tends to form a protective coating
over these hvdrophilic areas which is itself hydrophilic,
thus protecting and preserving the image and extending plate
wear. Alternatively, such coating may be applied prior to
the application of the hydrophobic layer material, as will
be discussed hereinbelow.
Applicator 20 applies a thin layer of a suitable
hydrophobic layer material through the action of a roll
stack on which extends across the width of roll 10. The
action of doctoring means 22, here-depicted as a roll 23
preceded by a water diet wash system 24, removes excess
material, and assures a thin, relatively uniform and
continuous hydrophobic layer of material on the surface of
roll lo Any suitable thickness of hydrophobic layer
material and means or method of application may be used. on
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many applications, however, a layer thickness which approaches monomolecular dimensions has been found to be
quite satisfactory and is preferred from the standpoint of
uniformity of application and ease of cleaning when using
many of the hydrophobic layer materials suggested end
discussed hereinbelow. Any method or means for applying
suitable quantities of the hydrophobic layer material which
results in relatively uniform and complete coverage of the
roll surface, and which does not contaminate the roll
surface, may be used. For example, an atomizer may be
employed. A preferred applicator, however, is a roll train
fed from a trough of the hydrophobic layer material,
immediately followed by a water flush and contact with 3
doctoring roll or blade, substantially as depicted in
Figures 1-4. It is generally advantageous to use
application techniques which result in the application of a
layer which is self-limiting in thickness, preferably
approximately monomolecular in thickness.
While any suitable material may be used to form the
hydrophobic layer of the plate, the material chosen
preferably should meet several requirements in order to
achieve the highest quality in the resulting printed image.
It preferably should be a material which, when applied to
the roll or plate in a thin layer, effectively renders the
roll or plate substantially uniformly hydrophobic and
oleophilic, by providing a hydrophobic and oleophilic layer
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thereon, which exhibits a relatively large wetting angle
with respect to the desired aqueous developer material used,
an affinity for the type of printing ink to be used, and
which is relatively durable. Equally important, it
preferably should be a material which has an affinity for
the roll surface and which can be applied in a thin, smooth
layer over the roll surface, as well as over small
quantities of any contaminants or residual material which
may be found thereon, without significant discontinuities or
open areas thereby forming a layer which is substantially
uniformly hydrophobic. Materials which can be applied in a
relatively uniform, homogeneous layer have been found to be
effective in providing a substantially uniformly hydrophobic
layer. It has been found that a layer of hydrophobic layer
material having a thickness which approaches or approximates
monomolecular dimensions and which appears to be adsorbed
onto the surface of the roll is quite effective, and is
generally preferred; for this reason, materials which
readily yield such layers, for example, as the result of
self-limiting application techniques, are generally
preferred. The descriptions which follow will speak in
terms of an adsorbed layer of material. It should be
understood that, while it is believed adsorbed,
monomolecular layers are achieved, somewhat thicker layers
may actually be resulting from the techniques described
herein. Under certain conditions substantially thicker
I
layers may be preferred (see, e.g., tetracosane, Table It
and discussion hereinbelow). A thin layer, hovers
generally easier to remove than a thicker layer, usually
results in fewer problems with generation of possibly
undesirable vapors, etc., and is therefore generally
preferred over a thicker layer of the same material. For
maximum versatility, the material may be one which does not
leave a residue upon heating to temperatures of about 345C
or above. It is thought that meeting this test assures that
the roll or plate coated with the material may be erased and
reimaged a large number of times without experiencing
problems with residue buildup. If generation of a longer
lasting image on the roll is desired, eta., if no periodic
reimaging is to be provided, it is desirable that the
material chosen be relatively unaffected by exposure to the
fountain solution or ink, to the atmosphere over the time
period during which the plate is to be used, or to whatever
gum-containing formulation is used. It is also recommended
that the material chosen be one which, after being applied
to the roll, does not readily migrate, i.e., does not
transfer itself either onto surfaces contacting the plate or
roll surface, or into hydrophilic areas on the plate or roll
surface. Unlike systems of the prior art, there is no
requirement that the material be photosensitive or
I photo-chemically reactive, or that the material be comprised
of a polymer, an oligomer, or a material which is subacute to
- 18 -
~32
polymerization, oligomerization, or cross-linking. Suitable
polymer or oligomer-containing or cross-linkahle materials,
may be employed if desired, however (see, e.g., polyvinyl
bitterly, Table I). There is also no requirement that the
material be readily dissolvable in a wash or developing
solution.
A variety of materials have been found to meet these
requirements. Table I lists typical examples of these
materials, along with the particular solvents used in the
application of these materials to the noted metal shim
stock, and the contact angles observed in laboratory contact
angle tests, as measured manually with an optical
comparator. The measured contact angle, which corresponds
to the wetting angle as defined by the Young equation, is an
inverse measurement of the spread ability or nettability of a
liquid - in this case, distilled water - on a solid surface
- in this case, the plate surface carrying a thin layer of
the material being tested. The lower the observed contact
or wetting angle, the more wettable the surface is by the
distilled water, and, presumably, the less suitable the
material comprising the layer may be as a hydrophobic layer
material for use with an aqueous fountain solution in a
lithographic-type printing process. The solvent
temperatures were approximately 22C unless otherwise
specified. The contact ankles were observed on a section of
Type 304 stainless steel shim stock which was pretreated by
- 19 -
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placement in a muffle furnace at approximately 345~C for one
minute. except where noted below, the shim was dipped
quickly in the solvent containing the recited concentration
of material, removed, quickly and thoroughly rinsed with
distilled water, and the contact angle measured. Several
trials for each material were performed. Angles marked with
an asterisk indicate that lower contact angles were obtained
on some trials with these particular materials; it is
thought these materials may be somewhat sensitive to the
uniformity of the application process.
In general, hexadecanoic and octadecanoic acids may be
preferred over their acid salts, because, among other
things, the relatively inferior volubility of these salts
can make uniform application difficult.
The ammonium and potassium salts are particularly
preferred among the preferred acid salts listed. The
preferred metal soaps are all salts of Starkey acid using
either aluminum, magnesium, or calcium cations, and were all
supplied by Witch Chemical Co., 277 Park Avenue, New York,
New York 10017.
The preferred anionic surfactants listed are products of
Room & Hays, Independence Mall West, Philadelphia,
Pennsylvania 19105. While the observed wetting angle of the
phosphate ester was relatively high, it is thought that a
phosphate residue may develop if the material is repeatedly
removed and reapplied, as where the printing plate is
reconfigured frequently.
- I -
~Z3;~0
Tetracosane is a preferred hydrocarbon wax which was
applied by dipping a shim in the hexane solution and merely
allowing the hexane to evaporate. While the resulting
applied layer was substantially thicker than the other
materials, tetracosane still exhibited a satisfactory
contact angle and is believed quite suitable for use in
printing applications where a thicker layer of material
would be advantageous.
The listed preferred ethoxylated carboxylic acids are
products of Glyco, Inc., 51 Weaver Street, PRO. Box 700,
Greenwich, Connecticut 06830.
The preferred carboxylic acid androids listed are the
reaction product of olefins and malefic android, and are
manufactured by Milliken Chemical, PRO. Box 817, Unman,
South Carolina 29349.
Elemental sulfur is an example of a preferred inorganic
or non-carbon containing material which may be used to form
a hydrophobic layer.
Polyvinyl bitterly is an example of a suitable polymeric
material is preferred. The sample used is marketed under
the name Butvar B-76, a product of Monsanto Plastics and
Resins Co., St. Louis, Missouri 63166.
The acrylic resin ACRYLOID B-44, distributed by Room &
Haas,Philadelphia, Pennsylvania, is another example of a
preferred polymeric material.
Returning now to the features of Figure 1, roll 10
passes roll stack 22 or similar means for assuring that a
thin, uniform layer of the chosen hydrophobic layer material
is being applied over the entire roll surface. For purposes
of explanation, if roll 10 were subjected at this point in
the process to applications of fountain solution and Leo
ink via roll stacks 40 and 50, respectively, roll 10 would
print solid ink.
In the embodiment shown, arranging the hydrophobic layer
material on roll 10, thereby forming a latent image, is
achieved by an imaging means which removes, e.g., by
ablation, selected portions of the hydrophobic layer in a
desired image-complementary configuration, thereby rendering
those areas relatively hydrophilic. Any suitable energy
means may be used as an imaging means to remove the
hydrophobic layer material in the manner intended. There is
no requirement that the energy means be sufficiently
powerful to change the nature of the underlying roll
surface. In fact, it is generally advantageous that the
nature of the underlying hydrophilic material remain
substantially unchanged, and it is an advantage of the
invention that such change is generally unnecessary. The
generally preferred energy levels are therefore those levels
which are sufficient to remove the necessary quantities of
hydrophobic layer material, without substantially affecting
the hydrophilic material thereunder, excepting possible
- I -
~3;~7~
minor pitting, etc. It is thought that, by removing
portions of the hydrophobic layer, a portion of the
underlying hydrophilic material is at least partially or
more nearly exposed, thereby creating an area which can be
wetted preferentially by an aqueous developer material such
as a fountain solution or an aqueous ink. It is observed
that, upon selective removal of at least portions of a
hydrophobic layer which coats the underlying intrinsically
hydrophilic roll surface, a latent image is generated,
presumably defined by contiguous hydrophilic and hydrophobic
regions respectively formed by the partially exposed
portions of underlying roll surface and the intact portions
of the hydrophobic layer. It should be noted that, unlike
systems of the prior art, no wash step or developing step,
using water, solvents, toners, or any other materials is
necessary to establish this latent image on the roll
surface. Additionally, it should be noted that the
formation of the latent image does not depend upon any
photo-induced reaction, for example polymerization,
cross-linking, or indeed any kind of chemical reaction as
would be used to harden, soften, or otherwise "cure" a
hydrophilic or hydrophobic layer, or render such layer
either soluble or insoluble during a conventional
post-exposure wash step or development step as might be
commonly done in systems of the prior art.
I Jo
Various energy means may be employed as the imaging
means to remove portions of the hydrophobic layer material
from the surface of roll 10. In the apparatus of Figure 1,
a stylus array is used, such as the one depicted in Figure
6, although electrode configurations other than a stylus may
be used. Stylus array 30 is a spaced array of individually
insulated and individually computer-addressable electrodes
or styli 32 which are arranged generally perpendicular to
and uniformly equidistant from the electrically conductive
surface of roll lo within an insulating form 34. The
adjacent styli spacing and total number of wire styli are
functions of the desired effective printing gauge - if
relatively fine, detailed lettering is desired, a high
stylus density is necessary. If stylus density is so high
that mutual interference between adjacent styli results and
inter-stylus definition is lost, several separate, closely
adjacent stylus arrays of more widely spaced styli may be
used in a staggered, overlapping configuration. In place of
a full-width stylus array, one or more styli may be
positioned in close proximity to the roll surface and
sequentially traversed across the roll face as the roll is
incrementally rotated, thereby allowing the roll surface to
be imaged without the use of a full width array of styli
depicted in Figure 6. If an imaging means which is not
suitably selectively addressable is used, a mask, stencil,
overlay, or the like, as depicted at 36 in Figure 6 may also
- 24 -
~Z3~7~
be used to block selectively the unintended removal of the
hydrophobic layer material; use of such a mask interposed
between the imaging means and the plate surface or the
hydrophobic layer thereon, may reduce the need for direct
computer control by allowing use of, for example, an array
of continuously energized styli or other broad coverage
electrode configuration sweeping the entire image area.
Such array would only remove portions of the hydrophobic
layer material in areas not blocked by the mask or stencil.
Imaging of the coated roll surface by the embodiment
depicted in Figure 1 is achieved by establishing an
electrical potential of several hundred volts between the
roll surface and one or more selected styli in the stylus
array, thereby causing a spark discharge to occur between
the respective tips of the selected styli and the roll
surface. The energizing electrical signals are routed to
the selected individual styli in an image-related
configuration. The term imaae-related is used to mean
either an image (i.e., ink-carrying) or image-complementary
configuration, and merely indicates that, regardless of the
type ink used, the hydrophilic and oleophilic areas of the
plate are arranged in a configuration from which the desired
ink image may be produced. Image configuration is generally
used with an aqueous ink (the ink conforms to the
hydrophilic areas of the plate), while an Leo ink requires
imaging of the complement of the desired ink ire (the ink
- 25 -
~3~7~)
is made to conform lo the hydrophobic area). Figure 1
depicts use of an Leo ink therefore the desired image
configuration is image-complementary.
The duration, polarity, and waveform of such signals may
be tailored to the particular application and apparatus.
The source of such signals, not shown, may be a digital
computer or other source of electronically-yenerated
imagery. Generally speaking, direct current signals at
moderate voltage levels (300-1000 volts) and low current
levels (less than 10 milliamps) have been wound to be
satisfactory. To avoid charge accumulation on the roll
surface and accompanying loss of potential, the surface of
the roll or plate may have relatively low electrical
resistance. Also, the polarity of the energizing signal may
be periodically reversed Introduction of an inert gas in
the arc region such as argon, neon, helium, or combinations
thereof, by means of conduit 26 in Figure 1 or by other
means, is helpful in reducing the required breakdown voltage
and in minimizing electrode erosion. A gas comprising 10/~
helium and YO-YO neon has been used with success. Other, more
expensive spark chamber-type gases may be used as well to
further reduce the voltage levels required.
Where rapid imaging of roll 10 is desired, it may be
difficult to initiate the necessary electrical discharge
without a substantial time delay between application of the
requisite voltage level and the initiation of the electrical
- 26 -
SKYE
discharge. This is thought to be due to the lack of
instantaneous availability of free electrons to initiate the
avalanche condition necessary for discharge to occur. It
has been found that, by "seeding" the region in which the
-5 discharge is to take place with charged particles, as from a
corona discharge device, as depicted at 28 in Figure 1, this
time delay can be substantially reduced. An ultraviolet
light source may also be employed in place of a corona
discharge device.
The resulting imaged plate is schematically depicted in
Figure 10, in a magnified perspective view, wherein roll 10
is supporting hydrophilic plate 11 on which is defined an
area 100 carrying a hydrophobic layer and an area 102 which
is the exposed surface Go plate 11. As will be explained
hereinbelow, a hydrophilic protective layer may be applied
directly to the surface of plate 11 in area 102, and which
may optionally extend within area 100.
An alternative embodiment of this invention, employing a
beam of electromagnetic energy as an energy means, is
schematically depicted in Figure 4. In the embodiment
shown, the energy of one or more incident laser beams from
laser system 60 is substituted for the spark discharge
described above, these beams being modulated or otherwise
allowed to selectively impinge on the layer of hydrophobic
layer material with sufficient energy to cause selective
ablation of portions of the hydrophobic layer in the desired
I
image-related configuration. One or more such beams may be
electronically modulated and, if necessary, traversed over
the plate surface. It is foreseen that laser system 60 may
be an array of closely spaced lasers, arranged in a pattern
analogous to the electrical styli discussed above. As
before, no photo-induced chemical reaction is believed to
contribute in any significant way in this imaging process.
Examples ~III and IX were conducted to demonstrate the use
of a laser beam to generate an image on an intrinsically
hydrophilic sheet having a hydrophobic layer thereon; it is
believed the imaged sheet of these examples could, if
installed on a suitable press, be used as a printing plate.
Other suitable sources of electromagnetic energy may also be
used, so long as the energy directed onto the hydrophobic
layer is sufficient to cause removal of portions of the
layer in the desired image-related configuration. A
stencil, mask or the like may be interposed between the
energy source and the plate, as discussed herein in
connection with other imaging means, if desired. Such a
mask or stencil would be advantageous if, for example, the
laser or other beam could not be suitably modulated to allow
proper formation of a satisfactory image.
It is also foreseen that other means for removing the
hydrophobic layer may be used. For example, one or more
jets of heated air or other fluid, controlled, for example,
by electrically actuated valves, may be positioned to direct
- 28 -
~3;Z~
a stream or streams of heated fluid onto the layer, thereby
selectively removing at least portions of the layer in the
desired image-related configuration, for example, by
vaporization or evaporation, and at least partially exposing
the hydrophilic material lying thereunder. In certain
applications, a group of well defined, focused streams may
be arranged into one or more arrays positioned and/or
actuated to impinge upon the hydrophobic layer in the
correct sequence to generate the desired latent image. One
or more individual streams may also be employed, with a
means for actuating or modulating and traversing or
otherwise positioning the streams relative to the
hydrophobic layer to form the desired latent image. In
other applications, it may be advantageous to employ one or
more relatively unfocused fluid streams which are directed
through a stencil, mask, or the like which is interposed
between the jets and the plate or the hydrophobic layer
thereon. The stencil or mask would be used to assist in
directing the fluid streams to the appropriate areas on the
hydrophobic layer and to prevent significant unintended
removal of the hydrophobic layer material.
Prior to the application of an Leo ink and following
the selective removal of portions of the hydrophobic layer
from the roll in image-complementary configuration, an
aqueous developing material, for example, a conventional
aqueous fountain solution, is applied tug the roll surface,
- 29 -
~'~3;~7~
by roller stack 40 or other suitable means. It is generally recommended that the fountain solution contain gum or the
like in amounts commonly found in commercial preparations.
If, however, a shortened plate image life is desired, as,
for example, where the plate is frequently reimaged with a
different image, distilled water or other aqueous liquid may
be used as a fountain solution. In either case, the
fountain solution adheres to the areas from which the
hydrophobic layer material has been removed, forming an
image on the roll surface which is the complement of the
desired Leo ink image.
To enhance the durability of the hydrophilic areas of
the image plate, a gum-containing formulation optionally may
be applied to the plate after the imaging step and prior to
the application of fountain solution. As discussed earlier,
the gum is attracted to the exposed hydrophilic areas and
tends to form a protective coating over these hydrophilic
areas which is itself hydrophilic. This effectively extends
the life of the image on the plate. the gum formulation may
be applied by any convenient means in any conventional
manner. Customarily, the application of such gum
formulation is accompanied by a water wash step in which
excess gum is removed. In many cases, a fountain solution
containing gum, if allowed to remain momentarily on the
imaged plate, is sufficient for use in this gumming step.
- 30 -
~Lf~327~0
Following the application of fountain solution, a layer
of an Leo marking material such as an Leo ink is then
applied in a conventional manner to the roll surface by
roller stack 50 or other suitable means; as is expected in
lithographic-type printing systems, the Leo ink adheres
only to those areas of the roll surface which are not
covered by the aqueous fountain solution. As shown in
Figure 1, the roll surface may then be pressed directly
against the moving surface of substrate 8 via impression
roll 6; alternatively, roll 6 may be an offset or blanket
roll 6 by which means the inked image is transferred to the
moving surface of substrate PA, as in conventional offset
printing technology. Other intermediate transfer devices
such as belts, etc. may also be employed. Substrate 8 or PA
may be comprised of paper, a textile material, or any other
suitable material. Any suitable means for moving substrate
8 or PA may be employed. If desired, the inked image may
also be fixed on the roll surface, without subsequent
transfer to a substrate.
In those cases where a plate roll is used, and
preferably where the roll surface is not merely supporting a
separate printing plate, but is in fact acting as the
printing plate itself, or where another endless surface such
as a belt is used to provide the plate surface, an image may
be formed in a continuous manner around the entire perimeter
of the roll or belt, with no gap or seam in the plate
- 31 -
3~232~
surface to produce a corresponding gap or seam in the
printed substrate. The printed image length need not be
confined to the length of the plate surface or to an
integral divisor of the plate roll or belt circumference as
is necessary in conventional rotary systems. The image
length may in fact exceed the plate roll circumference, or
the plate roll circumference may be some non-integral
multiple of the image length, due to the fact that portions
of the image can be continuously erased and reformed on the
roll or belt at the same time a previously formed portion of
the image on another side of the roll or belt is being
printed. Of course, rather than having the actual roll
surface serve as the printing plate, a separate thin,
perhaps disposable, sheet of intrinsically hydrophilic
material as discussed above may be secured to the perimeter
of the roll; this thin sheet of material, superficially
resembling a conventional lithographic plate, would then
serve as the ink image transfer surface rather than the roll
surface as described hereinabove. This separate sheet could
take the form of a continuous hollow cylinder or sleeve 11
which is secured to the plate roll 10, as depicted in Figure
5, or could alternatively resemble a conventional
lithographic printing plate. Also depicted in Figure 5 is a
mask 36 which may be employed in an imaging process.
Obviously, imaging around the entire circumference of such
plate would not be possible unless such plate in fact
extended completely around the plate roll.
- 32 -
~3~7~
A principal application of the teachings herein is in
the generation of a plate which is imaged one time, and then
run without further rummaging for a relatively large number
of plate impressions. Metals which are preferred in this
application include nickel, copper, tin, brass, zinc,
titanium, zirconium, aluminum, stainless steel, palladium,
platinum, lead, and gold. The use of gum preferably in a
separate gumming step to protect the hydrophilic areas of
the plate is recommended in this application.
A second application of the teachings herein is the
printing of images wherein the plate is sharpened or
refreshed, i.e. the hydrophilic nature of the hydrophilic
areas of the printing plate is rejuvenated. This may
require nothing more than energizing the imaging means
(e.g., electrical styli or other ablation means at the
appropriate time in the printing cycle and in registry with
the original image, after most of the ink and fountain
solution have been removed from the plate, and thereby
removing any scumming (i.e., ink or other undesirable
material) present in the hydrophilic or non-ink areas of the
plate.
It is also possible, however, and recommended in many
situations, particularly if excessive scumming is noted, to
clean the roll or plate down to its intrinsically
hydrophilic surface, redcoat the surface with an adsorbed
layer of hydrophobic layer material, and image the roll or
- 33 -
27~
plate with either the same or a different it a
reconfigured) image after a predetermined number of
revolutions of the roll. This can be regarded as a third
application of the teachings herein - the periodic complete
reimaging of the plate, with either the same or a totally
different, reconfigured image, during each revolution or
after a selected number of revolutions, of the plate roll.
Where complete reimaging of the roll or plate with a
reconfigured image is desired, one may wish to remove the
residual ink and hydrophobic layer material previously
applied before applying a fresh layer of the hydrophobic
layer material. A conventional roll cleaning means may be
used to remove the ink and fountain solution which has not
transferred to the substrate; alternatively, the press may
be run without ink resupply until most or all of the ink on
the plate has been depleted, and then run without fountain
solution resupply. An additional cleaning means may be
helpful in removing the hydrophobic layer material carried
by or adsorbed on the roll or plate, as well as any gum
formulation which may have been applied to enhance the
durability of the image. This additional cleaning means may
simply take the form of an additional imaging means, e.g., a
stylus array to which a lithographically "blank" pattern
(i.e., resulting in a totally hydrophilic roll surface) may
be directed, thereby requiring all styli to become
energized.
- 34 -
~23Z~
It is suggested that, in many applications, a single
imaging means may be used for both imaging and cleaning.
Referring to Figure 1, the roll cleaning process would
involve two sequential revolutions of roll 10, with roll 6
appropriately disengaged. During the first revolution, ink
is cleaned off the surface of roll lo by means of roll
cleaning and drying elements 12, 14, and 16, but the
hydrophobic layer applicator 20 and roll stack 22 are
disengaged, so that no hydrophobic layer material is applied
prior to the passage of the roll surface past the imaging
means 30 during this revolution. The imaging means 30 is
energized with a totally blank pattern, thereby effectively
cleaning the roll surface, i.e., substantially removing all
significant surface contamination, including hydrophobic
layer material and gum which may remain on roll 10 from a
prior imaging step. For best results, it may be necessary
to use energy levels somewhat higher than would be used or
preferred for normal imaging purposes, or to reduce the
speed of the roll surface during this cleaning step.
After passing the imaging station, the surface of roll
10 is now free of ink, fountain solution, hydrophobic layer
material, gum formulations, and any contaminants or foreign
matter, and is dry and entirely hydrophilic. The fountain
solution and inking applicators 40 and 50 are also
disengaged. The hydrophobic layer applicator 20 and
doctoring means 22 are then engaged, resulting in the
- 35 -
~'~3Z7~
application of a continuous, uniform layer of hydrophobic
layer material to the clean, hydrophilic roll surface. The
imaging, optional gumming, dampening, and inking steps are
then performed with roll 6 now pressing against plate roll
10.
If sharpening of an existing image without the
application of additional quantities of hydrophobic layer
material is desired, the imaging means 30 alone may be used
to remove, in registry, assorted material from the
hydrophilic areas of the plate, and thereby reduce scumming.
For best results, most of the ink and fountain solution on
the plate should be removed or allowed to become depleted
before the plate is reimaged by imaging means 30.
Additional energy may be required if excessive material such
as gum, etc., must be removed.
In the embodiment shown in Figure 2, it is assumed that,
unlike the embodiment of Figure 1, the image on the roll
surface is not replaced or sharpened at selected revolutions
of roll 10. Instead, the roll surface is imaged, and
multiple copies of that image are printed with no
reimaging. The initial revolutions of roll 10 may be used
to clean and image the surface of roll 10, as discussed
above. During this time, fountain solution and inking
applicators 40 and 50, and roll 6, may be temporarily
disengaged. If the hydrophilic roll material tends to
become contaminated with hydrophobic contaminants upon
~3~3~3
exposure to the atmosphere, the imaged roll may be gummed,
i.e., coated with a formulation containing gum or the like,
to establish a hydrophilic coating over the hydrophilic
areas of roll 10. Optionally, this coating may be dried
before inking and printing. If done promptly following the
imaging of roll 10, for example, and before any printing is
attempted, this coating will prevent the exposed portions of
the roll surface from becoming contaminated or undergoing
undesirable chemical reactions with the atmosphere, and will
have the effect of preserving the hydrophilic nature of
those portions of the surface of roll 10 from which the
hydrophobic layer material has been removed, thus
contra outing to a more durable image on the plate. In the
embodiment shown in Figure 2, this coating step may be
accomplished by relying upon the gum Arabic or the like in
the fountain solution, i.e., by engaging fountain solution
stack 40 immediately following the imaging of the surface of
roll 10, with ink stack 50 and the roll cleaning devices 12
and 14 disengaged, and, optionally, with solvent drying jets
16 in operation. This would require a full revolution of
roll 10 during which fountain solution containing gum would
be applied to the freshly imaged roll surface and optionally
dried, nothing more. Alternatively, a separate
aum-containing formulation may be used applied by means of
an appropriate applicator not shown in Figure 2, e.g., a
roll stack and doctoring roll, positioned immediately after
SUE
stylus array 30 and ahead of fountain solution applicator
40. To further render the plate more wear resistant,
oleo-type lacquer may also be applied in the presence of
water, which allows the lacquer to adhere only to the
hydrophobic areas.
After the desired image is placed initially on the
surface of roll 10 and any steps thought necessary are taken
to avoid potential oxidation or contamination of the exposed
hydrophilic surfaces, or to extend the life of the image,
the apparatus used (a) to clean the plate (i.e., solvent
roll stack 12, doctor blade 14, and solvent drying jets 16),
(b) to apply the hydrophobic layer material (i.e.,
applicator 20 and roller stack 22), and (c) to image the
resulting hydrophobic layer (i.e., stylus array 30, gas
conduit 26, and corona discharge device 28), are all
temporarily rendered inoperative. With these elements
I temporarily disengaged, the resulting system
superficially resembles a conventional printing system, in
which a fountain solution is applied (via roll stack 40) to
a surface bearing an image defined by hydrophilic and
hydrophobic areas, which in turn causes the Leo ink applied
subsequently by roll stack 50 to adhere to the roll surface
only where the hydrophobic areas repelled the fountain
solution. This inked image is then transferred to a
substrate as before, using roll 6 as an impression cylinder,
or as an offset roll. The inked roll is then replenished
- 38 -
~L2327~
with fountain solution and ink, via roll stacks 40 and 50,
respectively, and the process repeated. Like the embodiment
of Figure 1, and unlike conventional printing systems,
however, the hydrophilic areas are formed by the partially
exposed roll or plate surface, optionally coated with gum,
and the hydrophobic areas are formed by 2 single thin layer
of hydrophobic layer material which is selectively removed
from the roll surface without the use of light-sensitive
coatings, without any discernible polymerization,
cross-linking, or other chemical change to the material in
the hydrophobic areas, and without the need for any wash or
developing steps.
As suggested above, after imaging, the plate may be used
in a conventional manner, with conventional fountain
solutions, inks, etc. It is therefore contemplated that a
thin sheet of hydrophilic material as described above and
cut to appropriate dimensions may be coated and imaged as
disclosed herein, and placed in a conventional printing
press to generate the multiple printed copies desired. See
Examples I - VI. The device depicted in Figure 3, similar
to the device of Figure 1 but less the equipment necessary
for actual printing of the image (e.g., roll stacks 40 and
50, etc.), may be used for the plate generation and imaging
steps independent and apart from the actual printing
process, which process may be done on separate, conventional
equipment, long after the imaged plate is made.
- 39 -
~L~3~7~
Having thus outlined several embodiments of printing
apparatus and processes, and described various sequences of
operation, reference is now made to Figure 7 showing a
further embodiment. Unless otherwise noted, elements
similar to those previously described have been given the
same reference numerals and serve the same functions. In
the embodiment shown, the plate comprises an endless surface
in the form of a roll 10, which rotates in the direction of
arrow 86. Other forms of endless surfaces could be
lo employed, for example, belt-type ink transfer surfaces
arranged about a plurality of rolls. Various subsystems,
previously described, are arranged about the ink transfer
surface along its direction of movement. These subsystems
comprise: the cleaning subsystem 62, made up of elements
12, 14 and 16; the hydrophobic layer application subsystem
64, made up of elements 20 and 22; the latent image
generating subsystem, which may be generalized here as newly
numbered element 70; the aqueous fountain solution
application subsystem comprising element 40; the inking
subsystem comprising element 50; and the image transfer
subsystem comprising element 6, and, if desired, element 4.
In the discussion of previous embodiments, the substrate
to which the ink image is transferred comprises a web.
However, in accordance with conventional practice, the
substrate can comprise either a web or individual sheets as
desired. In the embodiment of Figure 7, individual sheets
- I -
are fed seriatim to the transfer station 6 by a sheet feeder
72 of any desired conventional design, as, for example, feed
rolls 74 and bin 76. The feed roll 74 removes the sheet
from the bottom of the stack and feeds it to the transfer
roll 6 wherein the ink image is transferred to the substrate
surface 8. The substrate is then fed to the output bin 78
wherein it is stacked unwept removal by a machine operator.
In the alternative, if roll 6 is used as an offset roll, the
ink image is transferred onto roll 6 rather than onto a
sheet between roll 6 and roll 10. The ink image is then
retransferred from the roll onto sheet PA which is fed by a
sheet feeder (shown in dotted lines) similar to the sheet
feeder 72. Elements 72, 74, 76, and 78 may be regarded as
comprising optional elements of the image transfer
subsystem. The latent image generating subsystem 70 can be
any suitable means, as discussed hereinabove, i.e., a
electrical spark discharge system, one or more beams of
electromagnetic energy, one or more heated fluid streams,
etc., and includes a source of image-forming signals, such
as a digital computer.
In a preferred approach, the latent image generating
subsystem 70 may be utilized in both forming the latent
image and in reimaging the roll surface. Alternatively,
however, a separate reimaging subsystem 88 may be employed.
The separate subsystem 88 can comprise a spark discharge
means or any other means as previously discussed in
- 41 -
~327~
reference to the literate image generating station 70, and may
be arranged, for example between the cleaning subsystem 62
and the hydrophobic layer application subsystem 64. A
primary function of reimaging subsystem 88 is to clean the
surface of roll 10 by removing hydrophobic layer material,
gum, etc., which may be present. This is achieved by
"imaging" the entire plate, resulting in a lithographically
blank, i e., totally hydrophilic, plate.
Each of the subsystems is selectively operable and their
respective operation is controlled by a control system 80.
The cleaning roll stack 12 and the doctor blade 14 are
actuated by moving them toward and away from the ink
transfer surface by means of mechanical actuators such as
solenoids or motors with screw drives 82. Similar actuators
I are also employed for moving toward and away from the ink
transfer surface the hydrophobic layer application subsystem
64, the latent image generating subsystem 70, the fountain
solution application subsystem on and the inking subsystem
50. Actuation of transfer roll 6 can be controlled by
controlling the sheet feeder 72 or, alternatively, the
transfer roll 6 can be moved out of engagement with the ink
transfer surface by conventional means. The drying jets 16
are controlled by means of electrically operated valves 84.
Accordingly, it is possible for the control system 80 to
selectively operate any of the various subsystems by
energizing the appropriate actuating systems 82, 84 or 72.
- 42 -
I I
Each time the ink transfer surface comes within operable
proximity to the complete sequence of subsystems, e.g., each
time roll I makes a complete revolution, may be termed a
cycle of operation.
The control system 80 may be implemented in any
conventional manner. For example, it is possible to utilize
conventional cam and switch arrangements for selectively
actuating the respective actuating systems 82, 84 and 72 to
provide any desired sequence of operation. Preferably,
however, in accordance with more current practice, a
digital-type control system would be employed utilizing a
programmable computer. The advantage of a digital-type
system is that a greater variety of operational sequences
can be selected. It is foreseen that the same computer
system may serve as both the control system and the source
of the electronically generated imagery to be printed.
Such a computer-type controller and associated actuating
systems could readily carry out on a single printing
apparatus, all of the various sequencing arrangements needed
to fully carry out the teachings herein. For example,
assume the system is required to place a latent image on the
previously described plate and print multiple, Leo ink
copies, using that same image. This mode of operation may
be termed "image and run." During a first revolution of
roll 10, cleaning subsystem 62 alone may be actuated to
remove ink or other material from the surface of roll 10.
- 43 -
~'~3Z~
During the second revolution of roll 10, latent imaging
generating subsystem 70 or separate reimaging subsystem 88
may be employed to clean the roll surface of hydrophobic
layer material, gum, etc. which may remain. Such actuation
of subsystems 62 and 88 ore optional, end may be eliminated
if the plate surface is sufficiently clean. Following the
optional passage of the roll surface past separate
reimaging subsystem 88, hydrophobic layer application
subsystem 64 is actuated, along with latent image generating
subsystem 70 and fountain solution application subsystem 64.
Ink subsystem 50 and the image transfer subsystem are not
actuated, to allow at least one revolution of roll 10
carrying nothing more than a gum-containing formulation
residing on an imaged plate. Applying fountain solution in
this manner can serve as an optional gumming step to enhance
the longevity of the hydrophilic portions of the plate, as
discussed earlier. Drying jets 16 may be optionally
employed at this point in the process. Of course, if a
separate gum-containing formulation is to be used, a
separate gum application and water jet wash subsystem 63,
schematically depicted at 18 and 19, respectively, in Figure
8, may be desired. Control system 80 could be modified
appropriately to accommodate the addition of such subsystem.
After the image on the plate has been generated and,
optionally, summed, only the fountain solution application
subsystem 40, inking subsystem 50, and the image transfer
- 44 -
~'~3~Z7'~
subsystems are actuated, which results in the printing of
the same image with each revolution of roll 10.
If a change in the image is desired at this point,
several options are available. If a complete reimaging of
the plate is desired and the plate has been gummed, a
preferred approach is to begin as above, with the actuation
of only cleaning subsystem 62, followed by activation of
latent image generating subsystem 70 or separate reimaging
subsystem I etc., in order to clean thoroughly the roll
surface. If no gum was used, the actuation of these latter
subsystems may be unnecessary, and in many cases a fresh
layer of hydrophobic layer material may be applied over the
existing hydrophobic layer, providing little or no ink
remains on the plate. The adsorbed character of the layer,
which contributes a self-leveling quality to the material in
layer form, along with the method of application, can result
in a suitable thickness of material being applied.
Following this reapplication of hydrophobic layer material,
the plate is then imaged, dampened, inked, and the image
transferred to the substrate, as before.
It should be noted that the above-described sequences of
actuation are but a few of the possible sequences which may
be found to be advantageous under various circumstances.
Other sequences may be employed, as desired, to achieve
improved printing operation.
- 45 -
~'Z;32'7~
The previously described process results in a printing
plate in which those areas of the hydrophilic plate surface
intended to carry an Leo ink are coated with a hydrophobic
layer material, while the non-image areas of the hydrophilic
plate surface are thought to be at least partially exposed.
Where desired, a layer of gum may be made to cover these
partially exposed areas, thereby rendering these areas more
durably and decisively hydrophilic. The method for
generating such a plate described previously may be
summarized as follows: (1) coat the hydrophilic plate
surface with a thin layer of hydrophobic layer material, (2)
selectively remove the layer in the desired configuration,
and, (3) as an optional step, coat the resulting plate with
gum, the gum ordinarily adhering only to the exposed
portions of plate surface. Alternative processes for
generating the above described plate, as well as alternative
printing plate constructions, however, are possible.
rho above plate comprising hydrophobic layer material
and guy in contiguous areas may be generated either by
selective rennoval of a uniform layer of hydrophobic layer
material, followed by a gumming step, as summarized above,
or, for example, by (1) covering the plate surface with a
thin layer of gum, (2) removing selectively portions of the
gum layer in a desired configuration and (3) coating the
resulting plate with a hydrophobic layer material. Many
hydrophobic layer materials will not readily cover the
- 46 -
I
remaining portions of the gum layer, but will instead
preferentially coat the now-exposed portions of the plate
surface. The result is a plate comprising hydrophobic layer
material and gum in continuous areas, as before. Note,
however, that (1) the removal step was performed on the gum
rather than the hydrophobic layer material, and (2) the
removal step involved tracing the complement of the
configuration used before.
An alternative method for generating plates similar in
general construction to those disclosed above, which also
results in the placement of hydrophobic layer material on
the plate in an image-related, predetermined configuration
comprises selectively applying the hydrophobic layer
material in the appropriate configuration, rather than
selectively removing the material from a uniform layer, as
has been described above. This method may be implemented
using, for example, an ink jet printing assembly or other
means which is supplied with a source of hydrophobic layer
material of appropriate viscosity rather than ink. Many of
the materials listed in Table I are suitable for this
application. The ink jet printing assembly may be
substituted for the hydrophobic layer application subsystem
64 and the layer-removal portion of the latent image
generating subsystem 70 in the apparatus of Figure 7. In
other words, in Figure 7, the hydrophobic layer application
subsystem 64 may be disengaged, and the latent image
- 47 -
Sue
generating subsystem 70 may comprise an ink jet assembly, or
an array of such assemblies, which applies the chosen
hydrophobic layer material in the proper configuration. The
use of a stencil, mask, or similar device may be used to aid
in properly configuring the hydrophobic layer material, as
before.
As suggested above, alternative plate constructions are
also possible. Where a durably-imaged plate is desired, for
example, a suitable plate may be generated by (1) covering
the hydrophilic plate surface with a thin underplayer of gum,
(2) coating the gum underplayer with a thin over layer of
hydrophobic layer material, and (3) selectively removing the
over layer of hydrophobic layer material in the desired
configuration, without substantially disturbing the
underlying gum. Depending upon the choice of materials, it
has been found that application of the hydrophobic layer
material while in the vapor state, and allowing the material
to condense onto the gum surface, or heating the hydrophobic
layer material prior to application, aids in the formation
of the requisite hydrophobic over layer recited in step (2).
The chemical properties of most gums, particularly their
significantly higher molecular weight, allow them to adhere
well to exposed portions of the plate surface. In most
cases, the gum layer is relatively more difficult to remove
and tends to remain intact compared with the hydrophobic
layer material, and the imaging energy may be readily
- 48 -
issue
adjusted to accomplish this layer-selective removal with
many combinations of gum -Formulations or similar materials
and hydrophobic layer materials. The result is a plate
wherein the hydrophilic areas are comprised of the
hydrophilic plate surface, crated by a layer of gum, and the
hydrophobic areas are comprised of the hydrophilic plate
surface coated with a layer of gum, which layer in turn is
coated with an over layer of hydrophobic layer material. As
suggested above, this same plate construction may be
achieved by selective addition of the hydrophobic layer
material over the gum in the desired configuration, via an
ink jet or other means, rather than selective removal of the
material from a uniform over layer. The use of an ink jet or
other selective applicator could also be employed to
generate a plate wherein the plate surface is first
uniformly coated with a hydrophobic layer material, followed
by the selective application of a hydrophilic layer of gum,
e.g., by ink jet, in an image-related configuration.
The printing processes described hereinabove have
generally assumed use of a substantially planographic
printing plate wherein the image areas of the plate comprise
regions which are relatively hydrophobic and wherein the
non-image or image-complementary areas of the plate comprise
regions which are relatively hydrophilic. In conventional
lithographic printing processes, an Leo ink is applied to a
plate surface which has been selectively wetted, in
- 49 -
~327~
image-complementary configuration, with an aqueous fountain
or dampening solution. The plates used in these processes,
however, are also suitable for use in printing systems
employing aqueous inks. In their simplest form, such
systems may be thought of as lithographic systems in which
an aqueous-type ink is made a component of the aqueous
fountain solution. Such composite solution may be applied
in the same manner and sequence as a conventional fountain
solution, e.g., through the use of roll stack 40 or other
suitable applicator. No ink is applied via applicator 50,
which may be disengaged. The ink carried in the fountain
solution is transferred to a substrate as before, i.e.,
either directly or via an offset roll or the like. Because
the ink now resides in the hydrophilic areas, rather than in
the hydrophobic, oleophilic areas as before, the image
"sense" of the plate must be transposed, i.e., the
hydrophobic layer material must now be configured in an
image-complementary configuration and the hydrophilic areas
of the plate must be in image configuration, rather than
vice versa, as before. Tilts means that the electronic image
generating means which controls the selective application or
removal of the hydrophobic layer material must be modified
to impart the desired signals to the imaging means. (As
discussed earlier, a more general term, "image-related
configuration', may be used to describe the configuration of
either the hydrophilic or hydrophobic areas. Alternatively,
- 50 -
I
the latent image may be said to correlate with the resulting
ink image, in that one either directly implies or is
complementary to the other.) The process of cleaning
aqueous ink from the roll may be somewhat different than in
the Leo ink case, the hydrophobic layer material should now
no longer have an affinity for the printing ink used, and
other obvious differences may be found, but the overall
printing process, as distinguished from the imaging process,
is otherwise substantially similar, and may be used in
situations where aqueous inks are advantageous.
Consideration of the alternative processes and plate
constructions, and use of aqueous rather than Leo inks, as
discussed above, does not change significantly either the
manner in which the various plates may be generated, imaged,
erased, reimaged, or used in a printing process, or the
apparatus which would be used to effect such operations, in
accordance with the processes and apparatus previously
described, except in ways which would be readily apparent to
those skilled in the art. Assume, for example, a
durably-imaged plate comprising a complete, specially gummed
underplayer and a configured over layer of hydrophobic layer
material is to be generated and run without reimaging in an
apparatus along the lines of that depicted in Figure 7. The
apparatus depicted in Figure 8 is similar to that depicted
in Figure 7, except that a hydrophilic layer applicator
subsystem 63, comprising gum applicator 18 and wash means
- 51 -
3~23;~
19, and appropriate actuators 82, have been added
immediately prior to the hydrophobic layer applicator
subsystem. The sequence for the previously described "image
and run" mode of operation may be followed, except that,
immediately prior to the actuation of hydrophobic layer
application subsystem 64, hydrophilic layer applicator
subsystem 63 is actuated, causing a uniform, thin layer of
the gum formulation to be deposited on the hydrophilic
surface of roll 10. Optionally, roll 10 may be allowed to
revolve one or more times to allow the gum formulation to
dry. Following this gum application step, all remaining
steps of the "image and run" mode of operation are followed.
If aqueous ink, added to the fountain solution, is to be
used rather than Leo ink, the principal necessary changes
to the above would be (1) disengagement of ink subsystem 50,
and (2) adjustment of latent imaging generating subsystem to
remove the hydrophobic layer material in image, rather than
image-complementary, configuration.
Reimaging of the plate discussed above is relatively
easy, particularly if an aqueous ink is used, due to the
uniform, somewhat tenacious layer of gum residing on the
plate surface and the ease with which the aqueous ink may be
removed via cleaning subsystem 62. Layer-selective removal
of the entire layer of hydrophobic layer material is readily
accomplished, for example, by activation of reimaging
subsystem 88. Reapplication of a gum layer, if
- 52 -
3L2~2~0
necessary may be accomplished via optional actuation of
hydrophilic layer application subsystem 63. The natural
self-leveling tendency of gum prevents excessive gum
build-up. All the reimaging steps above, as well as the
application of a fresh layer of hydrophobic layer material,
followed by reimaging and printing, could be achieved
within a single revolution of roll 10 if desired.
A non-planographic, gravure-type cylinder having a
contoured surface which is intrinsically hydrophilic, as
discussed herein, may be substituted for the planographic
plate roll discussed above, with the benefit of advantages
analogous to those discussed above. The physical
configuration of the surface may be among those ordinarily
chosen by those skilled in the art; the shape at the
depressions, cells, grooves, etc., which comprise the
contoured surface is not important. The term cell is
intended to include all such features. Beginning with a
substantially clean cylinder, the desired hydrophobic layer
material may be applied either by applying a thin, uniform
layer to the cylinder surface and selectively removing,
e.g., by ablation, material from the surface of those cells
intended to accept an aqueous developing liquid e.g., an
ink, or by selectively applying, e.g., by ink jet methods, a
coating or layer of material to the interior surface of the
desired cells. It should be noted that, preferably, the
material and application means are chosen to permit the
- 53 -
3L~3~
application of a monomolecular or near-monornolecular layer
of the material which coats the walls and floor, or portions
thereof, of the desired cells and conforms thereto. It is
not necessary the, the hydrophobic layer material fill, to
any significant extent, the cell interiors. Treating the
cylinder surface with a gum-containing formulation either
prior to application of the hydrophobic layer material or
after imaging, to enhance the durability of the cylinder
image, is optional. Figure 11 depicts a magnified
perspective view of a cross section of the surface of a
conventionally configured Grover roll 104 which has been
imaged by arrangement of a hydrophobic layer material over
its hydrophilic surface. Shaded roll cells 106 carry an
adsorbed, thin hydrophobic layer; unshaded cells 108 carry
no hydrophobic layer material, and are therefore comprised
of the exposed intrinsically hydrophilic material from which
the roll is made, or a hydrophilic protective layer such as
a gum layer. Boundary 109 indicates that only a portion of
an individual cell need carry the hydrophobic layer
material.
Once the roll has been thus imaged, printing may be done
in accordance with conventional Grover printing practice.
Application of an aqueous ink to the cylinder surface,
followed by a doctoring step, produces an ink image on the
cylinder comprised of the cells which do not contain the
hydrophobic layer material. The image is then transferred
- 54 -
327~
to a suitable substrate by conventional means, e.g., direct
cylinder-to-substrate contact. As discussed above, if an
Leo ink is used along with a separate fountain solution and
fountain solution applicator, the "sense" of the image on
the cylinder must be changed so that those cells intended to
carry ink also carry a quantity of hydrophobic layer
material.
The resulting Grover cylinder may be easily reused,
i.e., reimaged, by cleaning ink from the cells and surface
of the cylinder using conventional methods, and removing,
e.g. by ablation, all remaining hydrophobic layer material
or other material from the cells. After thus thoroughly
cleaning the cylinder of all dirt, coatings, etc., a fresh
quantity of hydrophobic layer material may be applied as
lo before, i.e., either selectively in the desired
configuration, or as a uniform layer for subsequent
selective removal. It should be noted that, with the
invention herein described, the possibility exists to
generate half tones by varying the individual intracellular
area coated by the hydrophobic layer material, i.e., the
amount of interior cell surface which is coated with a layer
of hydrophobic layer material within individual cells may
vary.
The various sequences of cleaning, imaging, printing,
reimaging, etc., and the automated manner in which these
processes may be carried out, as discussed above in
- 55 -
connection with planographic plates, are equally applicable
where a Grover roll is used, except for modifications which
will be apparent to those skilled in the art and which are
dictated by conventional Grover printing procedures.
A seamless cylindrical screen similar to that used in
conventional screen printing methods also may be substituted
for the planographic plate roll discussed herein, with all
of the advantages analogous to those discussed above which
are appropriate for such a screen system. A reusable screen
lo may be fashioned by installing a clean, open, relatively
fine mesh (for example, about 100 x 100 mesh or finer,
depending upon the desired viscosity of the ink, etc.)
unimaged screen having mesh elements comprised of an
intrinsically hydrophilic material, as discussed herein, on
an apparatus similar to that depicted in Figure 9. Rather
than a solid plate roll, a cylindrical, substantially hollow
revolving frame 90 is used driven by any convenient means
around which screen 92 is stretched. A suitable hydrophobic
layer material as disclosed herein may be applied to the
mesh elements comprising the mesh surface of screen 92 by
means of roll stack 20 or other suitable means. Doctoring
means 22, comprised of a water jet wash system 24 and a
doctoring or kiss roll 23, are intended to remove excess
hydrophobic layer material from screen 92. Other doctoring
or rneteriny devices, such as a soft doctor blade, could be
used as well. Rolls 97, 99 serve to prevent deformation of
- 56 -
I
screen 92, and may supply energy to rotate frame 90 and
screen 92 in the direction indicated. The uniform quantity
of hydrophobic layer material adhering to the surface of
screen 92 after passing doctoring means 22 may be
selectively removed by any convenient means, e.g., a laser
system 30, as discussed above and depicted in Figure 9.
Figure 12 depicts a magnified perspective view of a
cross-section of a printing screen 110 which carries a
quantity of hydrophobic layer material in the upper left,
shaded portion. The material it adsorbed on the wire mesh
in area 112, and does not occlude the screen openings 114;
wire mesh outside area 110, as depicted at 1167 remains
substantially hydrophilic. Following the selective removal
of hydrophobic layer material from the surface of screen 92,
ink is then applied thereto, as by roll train 50 or other
suitable means. A high surface tension, low viscosity
aqueous ink is generally preferred. The ink is held within
the screen interstices only in those regions of the screen
wherein the hydrophobic layer material has been removed, and
nowhere else. It should be emphasized that it is not
necessary that the hydrophobic layer material cover or fill
the selected interstices from which an aqueous ink or other
aqueous developer material is to be excluded. The layer
material may therefore be considered substantially
non-occlusive.The aqueous ink is then transferred to a
substrate, as explained above. It is foreseen, however,
- 57 -
I
that if a process resembling a conventional lithographic
process is desired, using a screen in place of a solid
lithographic plate, an Leo, lithographic-type ink may be
used, along with a suitable fountain solution or other
aqueous developer material. In this case, the Leo ink is
held within the screen interstices only in those regions of
the screen where the hydrophobic layer material remains.
Other techniques for removing the hydrophobic layer
material, as discussed above, may be used. Because it is
only necessary to arrange the desired quantity of
hydrophobic layer material on the screen in an
image-related, configuration, the hydrophobic layer material
may be selectively applied to the screen surface, as, for
example by using a ink jet-type system, as discussed above,
rather than uniformly applied and selectively removed. Use
of a gum-type treatment, either before application of the
hydrophobic layer material, or after imaging, is optional.
When a new image is desired, the screen may be cleaned
of ink, by any suitable method, and of all hydrophobic layer
material by, for example, use of an ablation means as
discussed above. After the screen has thus been thoroughly
cleaned and is once again completely open, the screen may be
imaged again, by appropriate arrangement of hydrophobic
layer material, as above, in the desired new configuration.
If, for example, non-continuous imaging or non-seamless
printing is desired, a non-cylindrical screen can be
- 58 -
employed as well, with appropriate modification to the
imaging and printing methods and apparatus. The various
sequences of cleaning, imaging, printing, reimaging, etch,
and the automated manner in which these processes may be
carried out, as discussed above in connection with
planographic plates and Grover rolls, are equally
applicable where a print screen as described herein is used,
except for modifications which will be apparent to those
skilled in the art and which are dictated by conventional
screen printing procedures.
The following examples are merely intended to
demonstrate some of the preferred embodiments of the present
invention, and in no way are intended to limit the scope of
the invention.
- 59 -
I
Example I
A five mix (0.005 inch thick plain stainless steel
sheet supplied by the Precision Steel Warehouse, Inc. of
Downers Grove, Illinois, was placed in a 600F oven for five
minutes to vaporize any surface contaminants which may have
been present on the sheet surface. The sheet was then
mounted on a grounded steel plate cylinder. A small amount
of a solution comprising 0.2 grams of hexadecanoic acid
dissolved in 100 ml distilled water and 100 ml isopropyl
alcohol was then wiped by hand onto a four inch by four inch
area in the central region of the sheet, thereby rendering
that area hydrophobic. The region of the sheet outside the
four inch by four inch area remained clean of contaminants,
and was therefore substantially hydrophilic.
A linear stylus array comprising tungsten wires
approximately 10 miss in diameter supplied by the California
Fine Wire Company, of Grover City, California, with an
adjacent wire spacing of approximately one-half inch, was
positioned so that the distance between the wire tips and
the stainless steel sheet surface was approximately three
miss. The wires were held in an insulating matrix of glass
filled epoxy and glass fiber reinforced board. Each wire
was connected through a 100,000 ohm resistor and a switch to
a +800 volt DO power supply. The cylinder carrying the
stainless steel sheet was rotated at a circumferential speed
of approximately four yards per minute while the switch to
- 60 -
~32~ 3
the wires was closed, completing the connection with the
power supply. The stainless steel sheet was held at ground
potential via contact with the grounded cylinder. Argon gas
was directed to the region of the wire tips, at a rate of
approximately 3 C.F.H. As the sheet surface passed under
the wires, electrical arcs occurred between the wire tips
and sheet surface, thereby imaging the surface. After a
single pass of the sheet under the wires, the switch was
opened and the sheet was removed from the cylinder and
stored in distilled water, to prevent oxidation or
contamination of the clean hydrophilic areas of the sheet
traced by the arcs.
Several hours later the sheet was removed from the water
and mounted in a Multilith 1250 Offset lithographic
Duplicator (distributed by A M International, Los Angeles,
California) in place of a conventionally prepared
lithographic plate. The duplicator was inked with Pontoon
Process Brown ink, (supplied by A M Multi graphics, a
division of A M International, My. Prospect Illinois The
fountain solution used was a solution of one part (by
volume) EM Duplicator Fountain Concentrate, supplied by EM
Printing Products Division, St. Paul, Minnesota, and 31
parts (by volume) distilled water. After mounting the
sheet, the duplicator was run in the normal fashion, with
the dampening rolls applying fountain solution to the sheet
surface, followed by the inking rolls applying ink to the
- 61 -
Z~7~
sheet surface. The fountain solution was observed to wet
only those areas of the four inch by four inch region where
the arcs had impinged. The ink, being immiscible with the
fountain solution, coated only the remainder of the four
inch by four inch region containing no fountain solution.
The rest of the plate, being uncontaminated, wet with the
fountain solution and therefore did not accept ink. The
inked image was transferred to the blanket cylinder where it
was transferred to paper. A clean, sharp, well-defined
image resulted on the paper which was the complement of the
area traced by the arcs, i.e., a four inch by four inch
inked region carrying unlinked lines corresponding to the
region traced by the arcs. The sheet was used to print
multiple copies on paper. No significant image degradation
was observed.
- 62 -
~23;~
EXAMPLE II
The procedures of Example I were followed 9 except as
noted below. A five mix thick plain aluminum sheet, from
the same supplier, was used in place of the stainless steel
sheet. The sheet was cleaned with alcohol and placed in a
600F oven for one minute to vaporize any surface
contaminants. After the sheet was imaged, it was removed
from the cylinder and a diluted solution of fountain
solution (Formula 100 fountain solution, distributed by AM
Multi graphics, My. Prospect, Illinois) and distilled water
in a volume ratio of 1:32 was applied and allowed to air
dry. The plate was not stored under water The next day
the plate was mounted on the press, and multiple copies of a
clean, sharp, well-defined image were recorded on paper,
with no discernible trace of image degradation. Intentional
fouling of the hydrophilic areas of the plate with ink
resulted in a self-cleaning action by the plate; printing of
clean, sharp, well-defined images promptly returned.
- 63 -
~'~3~7~
EXAMPLE III
A five mix thick plain stainless steel sheet supplied by
the Precision Steel Warehouse, Inc. of Downers Grove,
Illinois, was mounted on the plate cylinder of a Multilith
1250 Offset Lithographic Duplicator, made by A M
International, of Los Angeles, California, in place of a
conventionally prepared lithographic plate. A linear array
comprising parallel tungsten wires 10 miss in diameter and
spaced 25 wires per linear inch supplied by the California
Fine Wire Company, of Grover City, California, was
positioned so that the distance between the wire tips and
the plate was approximately three miss. The wires were held
in an insulating matrix of glass filled epoxy and glass
fiber-reinforced resin board. Each wire was connected
through a 100,000 ohm resistor to a +700 volt DO power
supply through a switch. Prior to mounting, the surface of
the stainless steel sheet had been immersed in a fifty per
cent (by weight) solution of sodium Stewart in distilled
water (prepared by heating the mixture to a temperature of
about 50C and cooling), and then rinsed with streams of
distilled water and briefly air dried, leaving the sheet
uniformly hydrophobic. The duplicator was inked with 0/S
IOTA Process clue fifteen per cent 23401 ink, made by
Sinclair and Valentine Kiwi of Charlotte, North Carolina.
The fountain solution used was a solution of 31 parts (by
volume) water and one part (by volume) RIP Craftsman
- 64 -
I
Fountain Solution Soft Number 290701, supplied by Research
for Better Printing Chemical Corporation, Milwaukee,
Wisconsin.
With the dampening and inking rollers disengaged from
the sheet, the plate cylinder was rotated at a
circumferential speed of approximately four yards per minute
while the switch to the wires was closed, completing the
circuit to the power supply. The stainless steel sheet was
held at ground potential via connection with the grounded
lo duplicator frame. Argon gas was directed to the region of
the wire tips at a rate of approximately 3 C.F.H. As the
sheet surface passed under the wires, electrical arcs
occurred between the wire tips and the sheet surface.
After a single pass of the sheet under the wires the
switch was opened, the plate roll speed was increased to
twenty yards per minute, and the dampening roll was brought
into operative engagement with the sheet. The fountain
solution wet only those areas of the sheet where the arcs
had impinged. After several revolutions of the plate
cylinder in operative engagement with the dampening roll,
the inking rolls of the duplicator were brought into
operative engagement with the sheet. The ink, being
immiscible with the fountain solution, was repelled by those
areas wet by the fountain solution, and coated the surface
of the sheet only in those areas not wet by the fountain
solution, i.e., those areas where the arcs had not impinged.
- 65 -
12~27~
The inked image was then transferred to the blanket cylinder
where it was then transferred to paper. A clean, sharp,
well-defined image was printed on the paper which was the
complement of that image traced by the arcs, i.e., the paper
showed a solid inked area with a series of sharp, inked
lines corresponding to the regions traced by the arcs. The
sheet was used to make multiple copies of the image; no
discernible degradation in image quality was observed. The
sheet was then cleaned manually with mineral spirits, and
the sheet was recrated with the sodium Stewart solution and
rinsed with distilled water, as before. The imaging and
printing processes described above were repeated. Again,
the result was a series of clean, sharp, well-defined images
of unlinked lines traced within a region of solid ink,
similar to those obtained earlier. There was no visible
trace of the earlier image.
- 66 -
I
EXAMPLE IV
The surface of a glass roll approximately 4 inches in
diameter and comprised of 6G'~; Allah and 40% Shea was first
cleaned with isopropyl alcohol and then wiped dry Then a
solution of 50% hexadecanoic acid and 50% isopropyl alcohol
(by volume) was applied with a cotton swab, and the excess
was washed off with a stream of distilled water, presumably
leaving a thin layer. After air drying, the roll was imaged
using a 10 mix diameter tungsten stylus, spaced 2.0 miss
from the roll surface. An electrical current of 8 milliamps
at +80û volts was established in a spark discharge between
the roll and the sty US, as the roll turned at a
circumferential speed of I yam, thereby causing the arc to
trace a line on the roll surface. Argon gas was fed into
the region of the discharge, at a rate of about 10 C.F.H.
and at essentially atmospheric pressure.
A mixture (by weight) of 1 part EM Duplicator Fountain
Concentrate, distributed by EM Printing Products Division,
St. Paul, Minnesota, and 15 parts of distilled water, was
applied to the general area of the roll surface carrying the
image and allowed to remain momentarily. A roller was used
to apply an additional quantity of the above solution, which
was observed to wet only the imaged area. A
lithographic-type ink (Offset Black BYWAY, manufactured by
Burnt wood Industries, Inc., of Addison, Illinois) was then
applied to the general area of the roll surface carrying the
- 67 -
7~q~
image via a roller. The ink adhered to the roll surface
only where the fountain solution had not wet the roll, i.e.,
in those areas which had not been imaged by the spark
discharge. The ink image was then transferred to paper. A
sharp, well-defined printed image was observed. Additional
quantities of fountain solution and ink were sequentially
applied to the general area of the roll surface carrying the
image, and the image again transferred to paper. As before,
a sharp, well-defined printed image was observed.
- 68 -
I
EXAMPLE V
A 4" x 1" section of five mix (0.005 inch) thick type
~04 stainless steel sheet supplied by the Precision Steel
Warehouse, Inc. of Downers Grove, Illinois, was rinsed with
a stream of isopropyl alcohol, air dried, and placed in a
fife oven for one minute to vaporize any surface
contaminants which may have been present on the sheet
surface. The sheet was then dipped in a solution comprising
0.2 grams of hexadecanoic acid dissolved in a solution of
100 ml distilled water and 100 ml isopropyl alcohol and
rinsed promptly in cold tap water, thereby rendering the
sheet hydrophobic. The sheet was then dried in a stream of
nitrogen gas and securely mounted on a grounded, steel
cylinder in order to image the sheet surface. A single
tungsten wire approximately 10 miss in diameter supplied by
the California Fine Wire Company, of Grover City,
California, was positioned so that the distance between the
wire tip and the stainless steel sheet surface was
approximately three miss. The wire was held in an
insulating sandwich of acrylic plastic. The wire was
connected through a 100,000 ohm resistor and a switch to a
DO power supply adjusted to deliver +800 volt pulses at a
frequency of 17 K~z. The cylinder carrying the stainless
steel sheet was rotated at a circumferential speed of
approximately 1.2" per second while the switch to the wire
was closed, completirlg the connection with the power supply.
- 69 -
I
The stainless steel sheet was held at ground potential via
contact with the grounded cylinder Argon gas was directed
to the region of the wire tips, at a rate of approximately 3
C.F.H. As the sheet surface passed under the wires, an
electrical arc occurred between the wire tip and sheet
surface. After a single pass of the sheet under the wires,
the surface was imaged and the switch was opened. The sheet
was removed from the cylinder, rinsed with a 1:15 solution
(by volume) of EM Fountain Solution, distributed by EM
Printing Products Division, St. Paul, Minnesota, and
distilled water. The solution was left standing on the
sheet for five minutes, thereby gumming the plate. The
sheet was then rinsed with distilled water and inserted in a
prepared cut-out in the central portion of a EM R-Type
plate, distributed by EM Printing Products Division, St.
Paul, Minnesota, which had been imaged previously with a
diagnostic pattern, thereby forming a "hybrid" plate. The
"hybrid" plate was then mounted in a Multilith l~50 Offset
Lithographic Duplicator (made by AM International, Los
on Angeles, California in place of a conventionally prepared
lithographic plate. The duplicator was inked with Pontoon
Process Blue No. 530-8000, (supplied by AM Multi graphics, a
division of AM International, My. Prospect, Illinois). The
fountain solution used was a solution of one part (by
volume) Roses Fountain Solution G-7A-V-Comb, supplied by
Roses, Inc., Lake Bluff, Illinois, and 31 parts (by volume)
- 70 -
distilled water After mounting the sheet, the duplicator
was run in the normal fashion, with the dampening rolls
applying fountain solution to the sheet surface, followed by
the inking rolls applying ink to the sheet surface. The
fountain solution was observed to wet only those areas of
the stainless steel insert where the arc had impinged. The
ink, being immiscible with the fountain solution, coated
only the remainder of the stainless steel insert containing
no fountain solution. The rest of the plate, it the
conventional, diagnostically imaged plate, was selectively
wet with the fountain solution as expected and, accepted ink
in the diagnostic image areas. The inked image carried by
the entire hybrid plate was transferred to the blanket
cylinder, where it was transferred to paper. A clean,
sharp, well-defined ink image resulted on the paper, which
included an unlinked line representing the area traced by the
arc on the stainless steel insert. The sheet was used to
print multiple copies on paper. No significant image
degradation was observed.
To determine the erasability of the plate, and its
suitability for reuse, the stainless steel insert was
removed from the hybrid plate and cleaned by hand using
Blankrola , distributed by AM Multi graphics, of My.
Prospect, Illinois. After air drying, the insert was rinsed
with isopropyl alcohol and again air dried. The shim was
securely remounted on the grounded steel cylinder at
Allah
approximately a 45 angle to the direction of cylinder
rotation. The plate was imaged as before, except that a
voltage of +950 volts was used and the cylinder speed was
fixed at 1.5 yards per minute. The resulting arced line
crossed the original arced line at approximately a 45
angle. The arcing process was repeated 4 times over the
same area. The shim was then rinsed with palmitic acid and
gently rubbed with a paper tissue. Following this. the skim
was rinsed with distilled water, then with the above
fountain solution, then with distilled water, and then dried
in a stream of nitrogen gas. The shim was inserted into the
same prepared cut-out to form the "hybrid" plate as above,
and remounted on the above lithographic duplicator.
Multiple copies were printed which showed the same clean,
sharp image as before, except that the original unlinked line
now had a small portion containing ink, corresponding to the
region traced by the second arc which had removed the gum
from that area and thereby allowed the hexadecanoic acid to
coat the area. In effect, this region had been erased.
To rummage the shim, the hybrid plate was removed from
the duplicator and the shim removed from the cut-out. After
manual cleaning with Blankrola, the shim was dried and
rinsed with isopropyl alcohol. The shim was then reimaged
as above, forming a line parallel to the direction of
cylinder rotation directly over the initial imaged line,
except that non-pulsating direct current was used. The shim
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~23;~7~
was then reinserted into the standard plate, as before, and
mounted in the duplicator. Multiple copies were printed
which showed the same clean sharp image that was originally
visible after the first arcing. The same unlinked line,
S corresponding to the area traced by the arc, appeared but
without the former ink containing area visible in the
previous print. In effect, this area had been reimaged.
I
EXPEL Al
The procedures of Example V were repeated, except that a
4" x 1" section of five mix thick aluminum shim stock, from
the same supplier, was substituted for the stainless steel
shim, with similar results.
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~3Z~
Example VII
A 4" x 1" section of five mix thick type 304 stainless
steel sheet, supplied by the Precision Steel Warehouse, Inc.
of Downers Grove, Illinois was placed in an oven at 650F
for one minute, then dipped in the hexadecanoic acid
solution of Example IV. The section was mounted on the
apparatus of Example IV, with the cylinder traveling at the
rate no 4.6 yards per minute, the imaging procedures of
Example IV were food. The gumming solution of Example
IV was applied and let dry. An ink/fountain solution
mixture comprising 60 ml of the above gumming solution and
10 drops of TERAPRI~T Blue R disperse dye, distributed by
Cuba Geigy Corporation, Greensboro, worth Carolina, was
applied to the sheet by a roller. The mixture adhered to
the sheet only where the spark had traced, and nowhere else.
The inked surface of the sheet was then pressed against a
sheet of paper, whereupon the ink transferred to the paper,
forming a clear, sharp image of the path traced by the
spark. Reapplication of the mixture to the sheet, and the
I subsequent transfer to paper, yielded similar results.
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EXAMPLE VIII
A stainless steel sheet and a copper sheet, each 5 miss
thick and each supplied by Precision Steel Warehouse, Ionic
of Downers Grove, Illinois, were separately illuminated by a
pulsed ruby laser manufactured by Apollo Lasers, Inc. of Los
Angeles, California. The laser had an average beam energy
of 3.5 Joules, a beam cross-sectional area of approximately
0.0123 square inches, and a pulse width of I nanoseconds.
The sheets were untreated before illumination, and therefore
carried a film of machining oils and other materials
associated with the manufacturing process which rendered the
sheet surfaces hydrophobic as observed with distilled water.
Immediately after illumination each sheet was dipped in
distilled water and quickly withdrawn. The distilled water
wet and adhered to each sheet in the precise area
illuminated by the laser; all other areas of the sheets
remained water repellent, indicating that the hydrophobic
layer had been selectively removed in a predetermined
configuration and a precise, well-defined
hydrophilic/hydrophobic image had been inscribed onto each
sheet.
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~'~3~7~0
EXAMPLE IX
The procedure of Example VIII was repeated, using 5 mix
sheets of zinc and aluminum by Alga Products of Dangers,
Massachusetts in place of the stainless steel and copper
sheets. Similar results were obtained.
While specific components of the present system are
disclosed above, many variations may be introduced which may
in any way enhance, improve, or otherwise affect the system.
While specific variations are given in this description,
modifications and ramifications which occur to those skilled
in the art upon reading this description are also intended
to be included herein.
o
EXAMPLE X
A small grooved roll similar to a rotogravure roll and
having 120 grooves per linear inch, arranged in
approximately a 45 helix was placed in an oven at iffy for
one minute to clean the surface. The roll was then dipped
in the hexadecanoic acid solution of Example V and
immediately rinsed with water. The roll was then imaged,
using the procedures of Example V, except the voltage was
- +950 volts, the series resistance was 200 calms. Four
short, evenly laterally spaced dashes were traced by the
spark. The roll was then squirted with an ink comprising
(by volume) owe distilled water and 50% Shafer Strip blue
fountain pen ink, distributed by Shafer Eaton, Fort
Madison, Iowa. A rubber doctor blade was used to remove
excess ink. The ink wet only those areas of the roll traced
by the sparks. The roll was pressed against a sheet of
paper. Four short, inked dashes were formed on the paper.
Multiple copies were produced. All images were clean and
sharp.
While specific components of the present system are
disclosed above, many variations may be introduced which may
in any way enhance, improve, or otherwise affect the system.
While specific variations are given in this description,
modifications and ramifications which occur to those skilled
in the art upon reading this description are also intended
to be included herein.
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~32~
EXAMPLE XI
A small section of stainless steel screen (120 x 108
mesh) supplied by McMaster-Carr, Inc., Elm Hurst, Illinois,
was first placed in an oven at 600F for one minute, then
briefly dipped in the hexadecanoic acid solution of Example
V. The screen was then promptly rinsed with water, and then
attached to the apparatus of Example V. The imaging
procedures of Example IV were followed. The screen was made
wettable in the area traced by the spark. The imaged screen
was then dipped in distilled water to which a small quantity
of Pelican Yellow drawing ink distributed by Pelican AGO
Hangover, West Germany, had been added. Only the area
traced by the spark held ink. The screen was then pressed
against paper, and a clear, sharp image was transferred.
Repeated images were printed, with only ink resupply
necessary.
While specific components of the present system are
disclosed above, many variations may be introduced which may
in any way enhance, improve, or otherwise affect the system.
While specific variations are given in this description,
modifications and ramifications occur to those skilled in
the art upon reading this description are also intended to
be included herein.
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