Note: Descriptions are shown in the official language in which they were submitted.
~l2ZZ4~;~
Case 1484
PRINTING METHOD AND APPARATUS
BACKGROUND OF THE INVENTION
This invention relates to printing systems us;ng 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 transferrable 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 gravure 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
~aZ22~2
level as the rest of the plate. Rather than depend upcn the
re1ative elevation of portions of the plate surface to
define the ink-bearing image, planographic svstemS depen(l
upon certain areas of the plate having a greater rPlative
affinity fnr water than is shown by the remaining areas or
the plate.
In a typical lithoaraphic printing system, the relative
irnmiscibili-ty of grease and water is used to define and
maintain the image and non-image areas of the printing
plate. In stan~ard lithographic print.ing systems where
greasy-type or oleo inks are used, the lithographic plate is
made oleophilic (grease-lovina) and hydrophobic
(water-hatiny) in image areas (i.e., those ar(?as which will
receive and transfer ink to the paper sheet or other
material to be printed), and hydrophilic (water-loving) in
the non-imaye areas. These latter areas, which are in
image-complernentarv configuration, are sometinnes re-ferred to
as "lithographically blank" areas, because they normally
carry or transfer no ink. So long as sufficient wat:er is
2~ present in these lithographically blank areas, no nleo-type
ink will adhere tn t.he plate in these non-image areas. ~y
this arrangement, these hydrophilic, image-complementary
areas of the plate will retain preferentially an aqueous
fountain or dampen;ny fluid applied to the plate to the
exclusion of the remaininy portions of the plate, and will
thereby allow the greasy ink applied thereafter to a-~here
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only to the oleophilic areas of the plate intended to carry
the ink image.
Various techniques have been de~eloped for establishing
the hvdrophilic and hydrophobic areas of the printing plate.
The mos-t popular rlethod of establishing such image-deFining
areas is with the aid of light sensitive materials which
tend to undergo chenlical reactions when exposed to actinic
light. In a typical process, when using negative-imaged
films, the so-called "negative" plate is covered with a
layer nf a light sensitive diazo or photopolymeric
formulation. Strong light energy passing through the
neqative film and s-triking the plate causes the diazo or
photopolymeric formulation in the exposed or ima(led areas of
the plate to urldergo a chemical change, e.g., to polymerize,
formirlg thereby a hardened, hydrophobic, inl< receptive area.
The non-polymerized fornlulation 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 formulatinn containing gum arabic, carboxymethyl
cellulose guln, or the like. Often, the non-polymerized
formulation is washed away and the gum added in a single
step. If a long wearing plate is desired, a thin film of a
gum-con-tairling material may be rubbed onto or ntherwise
applied to the plate and the plate surface washed with
-- 3
~;~2~43~2
water, therehy 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. ~xposure of the plate, via the positive
film, then results in degradation of the coating in what
will be the imatJe-complenlentary (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
~5 an intermediate film transparency. In either case, however,
it is usually necessary that the resulting plate be
22~
developed and rinsed and a finishing solution usually must
be applied.
Electrostatic systems for generatinq 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
photoconductive 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 de~elop the plate, a
toner carrying a charge opposite to tha-t of the remairling
charged areas of the plate is then applied and made to sti~k
to the plate surface. ~fter fusin~q, the toned areas become
hydrophobic, while the untoned 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
prncesses of conventional design, generally exhibit
substantial deficiencies which are well known and commonly
encountered itl the printina industry. Representative of
these deficiencies are the following:
1) inabilitv to generate a high quality
lithographic~type printing plate without film preparat.ion
steps or without elaborate plate exposure and development
procedures;
12~2~
2) inability to reconfigure completely the image being
printed by the plate without substant:ial interruptinn of the
printing process or substitution of a second plate carrying
the desired reconfigured image;
3) inability to refresh or renew the nleophilic 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 ma-teria'l from
the plate surface or by f'oreign mat.ter residing on the
plate surface - without substantial interruption of the
printing process;
5) inability to correct substantial reaistration errors
in the plate without re-plating;
6) inability to print a continuously repeating pattern
on a web substrate using a rotary-type press without a yap
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 d;vide into the plate length or circumference
of the plat.e roll;
8) inability to eliminate roll shock i.e. the
?5 mechanical interaction between the respective gaps of the
plate and blanket rolls in rotary offset printing methods
which limits press speedsi
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9) inability to proof conveniently a freshly generated
plate under true production cond;tions, using production
inks, papers, etc.;
10) inability to stnre the equivalent of a large
library of printing plates for short or periodic printing
runs WitilOUt 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 from a source of electronically-generated images
such as a digital computer.
Attennpts 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 photolithographic techniques, such as halation
(i.e., imperfect light exposure caused by the reflective
nature o-F the printing plate supportin~ 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
~IL222~
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 pre-determined
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. Alternat;vely, 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 imaye corresponding to the desired
printed image is initially formed. This surface generally
will be the surface on which a pre-ink latent image, i.e.,
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",
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an image defined in terms of adjacent hydrophilic and
hydrophobic areas, is also initially formed The term
"imaging" is intended to mean the generation of this latent
image, prior to the application of ink.
~escribed 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
embodiecl image may be impressed directly onto the plate,
without requiring the use of photosensitive materials or
]~ coatings, or without elaborate developing steps. In
addition~ the disclosed surface is re-usable, in the sense
that a lithographic plate, for example, when imaged and used
for printing in accordance ~ith the teachings of this
invention, may be re-imaged 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
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 capahle of recordin~ an image defined
in ternls of hydrophobic and relatively hydrophilic areas;
such a s~lrface may be the ink transfer surface associated
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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
S of a planar surface, a cylinder, an endless belt, or other
form. It 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 methnd and appara-tus is herein disclosed which can
completely eliminate the costs assnciated with generating a
plate usin~ conventional photolithographic techniques~ as
well as the costs involved in maintaining a converltional
plate library for short-run or periodic printing jobs. The
necessity of replacing a plate when a sharpened, or slightly
modified, or totally reconfi~ured image is desired is
completely elirninated. The costs and limitations associated
with having gaps in the pla-te used in rotary-type presses
ZO 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 imaginq a separately attached
printing plate of conventional design. Additionally, a
series of pre-production run proofs may be generated
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: L~2;24~
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 adjus-tments as the final
production run, thereby eliminating any doubt whatsoever as
to the appearance of the Final printed image. Whatever
adjustments are necessary to develop a satisfactnry proof,
regardless of their magnitude, can be made to the plate
without removing the plate frnm the press, or having tn 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,
millimal costs for plate preparation, set up, storage, or
inventory are desired, or where no gap nr seam between plate
images on a continuous printed substrate is desired.
~ecause 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 followin~ detailed description in which reference is
made to the Figures sumnlarized below.
DESCRI~TION OF DRAWINGS
Fi~ure 1 schematically depicts a rotary printing system
usin~ printing plate described herein is being continuously
erased and re-imaged by means of an electric spark discharge
- 1]. -
~Z~A~ ~
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
re-imaged, but is being used to make a series of ;mpressions
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;
Fi(]ure 5 schematically depicts a plate, attached to a
~S plate roll, embodying the teachings herein, as well as a
mask wh1ch may be used in imaging the plate;
Figure 6 schematically depicts a stylus bar, comprised
of individually addressable styli, o~ a type suitable for
;maging printing plates herein described according to the
~0 teachings herein;
Figure 7 schematically depicts a rotary
lithographic-type printing system employing d control system
for correctly sequencing and controlling a variety of
operations directed to imaging, re-imaging, or printing an
image on a substrate according to the teachings herein.
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24~l2
Figure ~ 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 magni-fied perspective
cross-section of an imagecl planographic plate surface.
Figure ll schematically depicts a magnified perspective
cross-section view of a portion of a gravure 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 re-imayed with the
same or a different image or pattern ~t the same time a
substrate ~ is being printed. As suggested above, the plate
nlay 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 oleo ink is employed, will
~5 be explainecl beginning with cleaning roll stack 12. 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 16, removes all 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 prnduce a totally "blank" or
hydrophilic plate, as will be discussed later. SimilAr
procedures may be employed if removal of gurll is desiredl 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
signifi(:ant contamination, is substantially hydrophilic.
Any suitable intrinsically substantially hydrol)hilic
material may be 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-me~allic materials such as an aluminum oxide/titanium
dioxide composite (60% A1203, 40% Tin2), and mixtures
thereof. While any suitable intrinsically hydrophilic
rnaterial may be used with this invention, stainless steel
and alulninlllll are particularly suitable for many
~Z2~1~
applications. If, under some circumstances, the roll
material chosen tends to form a relatively hydrophobic
coatiny (e.g., a coating of airborne contaminants, etc.)
upon e~posure to the atmosphere, it may be desirable to coat
the roll surface with a layer of a suitable protective
material, for example, a num formulation containing gum
arabic, carboxymethyl cel~ulose gum, or the like, which
formulation will herein be referred to simply as "gum."
Such coating is also recomnlended if maximuln longevity of the
image on the roll is desired. If done immediately following
the imagina process, the 9U~l is attracted to the exposed
hydrophilic areas and tends tu form a protective coating
over these hydrophilic 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 nf 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 20 which extends across the width of roll 10. The
action of doctoring means 22, here depicted as a roll 23
preceded by a water ~iet wash system 24, removes excess
material, and assures a thin, relatively uniform and
continuous hydrophobic layer of material on the surface of
roll 10. Any suitable thickness of hydrophobic layer
material and means or method of application may be used. In
~2224~2
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 and
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 a
doctoring roll or blade, subs-tantially 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 hi~hest 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
~Z~2~2
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
monomoleclllar dilmensions 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 techn;~ues, 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 technigues described
herein. Under certain conditions, substantially thicker
~Z2;~:4~2
layers may be preferred (see, e.g., tetracosane, Table I,
and discussion hereinbelow). A thin layer, however,is
generally easier to remove than a thicker layer, usually
results in fewer problems with g~neration 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
re-imaged a large number of times without experiencing
problems with residue buildup. If generation of a longer
lasting image on the roll is desired, e.a., if no periodic
re-imaging 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-containinq formulation is used. Tt 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 pr-ior art, there is no
~ requirenlent that the material be photosensitive or
¦ 25 photo-chemically reactive, or that the material be comprised
of a polymer, an oligomer, or a material which is subject to
- 18 -
~L22~ 2
polymeri~ation, oligomerization, or cross-linking. Suitable
polymer or oligomer-containing or cross-linkable materials,
may be employed if desired, however (see, e.g., polyvinyl
butyral, 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
requirelnents. Table I lists typical exampl~s 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 spreadability or wettahility 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 wettahle the surface is by the
distilled water, and, presumably, the less suitable the
material comprising the layer may be as a hydrophobic layer
materi~l for use with an aqueous fountain solution in a
lithographic-type printing process. The solvent
I temperatures were approximately 22C unless otherwise
¦ 25 specified. The contact angles were observed on a section oF
Type 304 stainless steel shim stock which was pre-treated by
- 19 -
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W ~, t, t, ~ ~, tt, ~ ¢
~ ~ ~ t~
~ ~ ~ ~ o ~C ~ ~ C~
¢ ~ ~ e ~ u~ . ~ c
~) ~1 >~ q ' t/) O
.~ " æ ~ ~c ~ t ~ o ,, ~ ~ .,,
N ~ æ ~ t~ ~
1--1 a) ~1 ~ h ~t; 11 W Cl; ." W ~rl O
O ~ ~ ~ æ u~ ~ x ~; ~ 0
~ ~ t~ ~ o O ~1 ~ O ~ h C
¢ X c~ a~ o u~ æ ~ o ~ o o c~
~ O E~ u~ p~ ¢~
.
-l9c-
~l :
~2~2~
placement in a muffle furnace at approximately 345C 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 rontact angle measured. Several
trials for each material were perfnrmed. 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
1n uniformity of the application process.
In general, hexadecanoic and octadecanoic ~cids may be
preferred over their acid salts, because, among other
things, the relatively inferior solubility of these salts
can nnake uniform application difficult.
The ammonium and potassium salts are particularly
preferred among the preferred acid salts listed. The
preferrecl metal soaps are all salts of stearic acid usiny
either aluminum, magnesium, or calcium cations, and were all
supplied by Witco Chemical Co., 277 Park Avenue, New York,
New York 10017.
The preferred anionic surfactants listed are products of
Rohm & Haas, Independence Mall West, Philadelphia,
Pennsylvania 19105. While the observed wetting angle of the
phosphate ester was relatively high, it is thought that a
pnosphate resiclue may develop if the material is repeatedly
removed and reapplied, as where the printing plate is
reconfigured fre~uently.
- 20 -
~2~
Tetracosane is a preferred hydrocarbon wax which WdS
applied by dipping a shim in the hexane solution and merely
allowiny the hexane to evaporate. While the resulting
applied layer was substantially thicker than the other
materials, tetracosane still exhibited a satisfactnry
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, P.O. Box 700,
Greenwich, Connecticut 06P,30.
The preferred carboxylic acid anhydrldes listed are the
reaction product of olefins and maleic anhydride, and are
manufactured by Milliken Chemical, P.O. Box 817, Inman,
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 butyral is an example of a suitable polymeric
2n material is preferred. The sample used is marketed under
the name Butvar B-76, a product of Monsanto Plast;cs and
Resins Co., St. Louis, Missouri 63166.
The acrylic resin ACRYLOID B-44, distributed by Rohm &
Haas,Ph;ladelphia, Pennsylvan;a, is another example of a
preferred polymeric material.
- 21 -
2~
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 oleo
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
- 2? -
~222~12
minor pitting, etc. It is thought that, by removingportions 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
thata upon selective removal of at least portions of a
hydrophobic layer which coats the underlying intrinsically
hydrophilic roll surface, a latent irnage 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 establ;sh this latent ;mage on the roll
surface. Add;tionally, it should be notecl that the
formation of the latent image does not depend upon any
photo-;nduced react;on, 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
e;ther soluble or ;nsoluble dur;ng a conventional
post-exposure wash step or development step, as might be
commonly done in systems of the prior art.
- ,3 -
~222~2
Various energy means may be employed as the imaging
means to remoYe 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 un;formly equidistant from the electrically conductive
surface of roll 10, within an insulating form 34. The
adjacent styli spacing and total number of wire styli are
funct~ons 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 allow;ng 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
24~
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 allowiny 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 imaqe-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 oleo ink requires
imaging of the complement of the desired ink im~ge (the ink
- 25 ~
Z~12
is made to conform to the hydrophobic area~. Figure 1
depicts use of an oleo 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-generated
imagery. Generally speaking, direct current signals at
moderate voltage levels (300-1000 volts) and low current
levels (less than 10 milliamps) have been found 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 reg;on 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 rninimizing electrode erosion. A gas compris;ng lOYo
helium and 90Y neon has been used with success. Other, more
expensive spark charnber-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 -
~2224~l~
discharge. This is thought to be due to ~he lack ofinstantaneous availability of free electrons to initiate the
avalanche condition necessary for discharye to occur. It
has been Found that, by "seeding" the region in which the
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 magnif;ed 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 of 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 systenl Ç0 is substituted for the spark discharge
described above, these beams being modulated or otherwise
allowed to selectively impinge on the layer of hydrophobic
layer mater;al with sufficient energy to cause selective
ablation oF portions of the hydrophobic layer in the desired
- 27 -
12
image-related configuration. One or more such beams may be
electronically modulated ancl, if necessary, traversed over
the plate surface. It is foreseen that laser system 60 may
be an array of closely space~ 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 VIII 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 pr1nting plate.
Other suitable sources of electromagnetic energy may also be
used, so lnng as the energy directed onto the hydrophobic
layer is sufficient to cause removal of portions of the
layer in the desired imaae-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 des;red. 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 -
~ILZ224~
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 rela-tive 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 ~naterial.
Prior to the application of an oleo ink, and following
the selective removal of portions of the hydrophobic layer
from the roll in image-complernentary configuration, an
aqueous developing material, for example, a conventional
aqueous fountain solution, is applied to the roll surface,
- 29 -
~2;~24~2
by roller stack 40 or other suitable means. It is generally
recommended that the fountaîn 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 re-imaged 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
]0 image on the roll surface which is the complement of the
desired oleo 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 wh;ch is itself hydrophilic. This effectively extends
the life of the image on the plate, The gum formulation may
be appllecl by any convenient nneans 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 -
~2~2~2
Following the application of fountain solution, a layer
of an oleo marking material such as an oleo 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 oleo 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
a~ainst 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 8A, as ;n conventional offset
printing technology. Other intermediate transfer devices
such as belts, etc. may also be employed. Substrate 8 or 8A
may be comprised of paper, a textile material, or any other
suitable material. Any suitable means for moving substrate
8 or 8A 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 -
~L~22~2
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 sys-tems. 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
1~ 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. nf 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
S, 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 -
~2~2~2
A principal application of the teachings herein is in
the generation of a plate which is imaged one time, and then
run without further re-imaging ~or a relati~ely 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 gurn preferably in a
separate gumming step to protect the hydrophilic areas of
the plate is recommended in this application.
1() 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 re~juvinatecl. This may
require nothing more than energi~ing 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
~l 25 hydrophilic surface, recoat the surface with an adsorbed
layer of hydrophobic layer material, and image the roll or
- 33 -
~IL2;~2P~L2
plate with either the same or a different (i.e., a
reconfigured) image after a pre-determined number of
revolutions of the roll. This can be regarded as a third
application of the teachings herein - the periodic complete
re-imaging 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 re-imaging of the roll or plate ~ith 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 re-supply until most or all of the ink on
the plate has been depleted, and then run without fountain
solution re-supply. An additional cleaning means may be
helpful in removing the hydrophobic layer material carried
bi 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
~ e., resulting in a totally hydrophilic roll surface) may
be directed, thereby requiring all styli to become
energized.
- 34 -
1222~
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 f;rst 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 w;th 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
5p~ed 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
~, .
niaterial, gum formulations, and any contaminants or foreign
matter, and is dry and entirely hydrophilic. The fountain
solution and ink;ng applicators 40 and 50 are also
~lsengaged. The hydrophobic layer applicator 20 and
doctorlng means 22 are then engaged, resulting in the
~ - 35 -
~2~
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
materi~l 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 re-imaged by imag;ng 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 lO. Instead, the roll surface is imaged, and
multiplé copies of that image are printed with no
re-imaging. The initial revolutions of roll 10 may be used
to clean ancl 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
becom~ contaminated with hydrophobic contaminants upon
- 36 -
~222412
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 o-f 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
contrihuting 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 ima~ing of the surface of
roll 10, with ink stack 50 and the roll cleaning devices l2
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
- 37 -
~2~3 2
stylus array 30 and ahead of fountain solution appl;cator
40. To further render the plate more wear resistant,
oleo-type laquer may also be applied in the presence of
water, which allows the laquer 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
(a)-(c) 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 oleo ink applied
subsequently by roll stack 50 to adhere to the roll surface
only where the hydrophobic areas repelled the fountain
solution. This inkecl 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 -
~224:~2
with fountain solution and ink, via roll stacks 40 and S0,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 a 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 ir.
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 ~0 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
equipnnent, long after the imaged plate is made.
- 39 -
Having thus outlined several embodiments of printing
apparatus and processes, and described various seguences of
operation, reference is now made to Figure 7 showing a
further embodiment. Unless otherwise noted, elements
5 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
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
nùmbered element 70; the aqueous fountain solution
application subsystem comprising element 40; the inking
20 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
25 substrate can compr;se either a web or individual sheets as
desired. In the embodiment of Figure 7, individual sheets
- 40 -
~Z22~2
are fed seriatum 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 rennoves 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 until 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
re~transferred from the roll onto sheet 8A 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 re-imaging the roll surface. Alternatively,
however, a separate re-imaging subsystem 88 may be employed.
The separate subsystem 88 can comprise a spark discharge
means or any other means as previously discussed in
- 41 -
~;~22~2
reference to the latent 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 re-imaging subsystem 88 is to clean the
surface of roll 10 by removing hydrophobic layer material,
gum, etc., wh;ch 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
82 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 4n and the inking subsystem
50. Actuation of transfer roll 6 can be controlled by
controlling the sheet feeder 72 or, alternat;vely, 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 electric.ally 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 -
~%2~412
Each time the ink transfer surface comes within operable
proximity to the complete sequence of subsystems, e.g., each
time roll 10 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 ~2, 84 and 72 to
provide any desired sequence of operation. Preferably,
however, in accordance with more current practlce, 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
pre~iously described plate and print multiple, oleo ;nk
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 -
1~%Z412
During the second revolution of roll 10, latent imaging
generating suhsystem 70 or separate re-lmaging subsystem 88
maY be employed to clean the roll surface of hydrophobic
layer material, gum, etc. which may remain. Such actuation
of subsysterns 62 and 88 are optional, and may be eliminated
if the plate surface is sufficiently clean. Following the
optional passage of the roll surface past separate
re-imaging 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 acconlmodate the addition of such subsystem.
After the image on the plate has been generated and,
optionally, gummed, only the fountain solution application
subsystem 40, inking subsystem 50, and the image transfer
- 44 -
~2Z;i~41~
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 re-imaging 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 re-imaging
subsystem ~, etc., in order to clean thoroughly the roll
surface. If no gum was used, the actuation of these latter
subsyskems may be unnecessary, and in many cases a fresh
layer of hydrophobic layer material may be applied over the
exist;ny 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 re-application 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 hut 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.
- ~5 -
~;~2Z4~
The previously described process results in a pr;nt;ng
plate in which those areas of the hydrophilic plate surface
intended to carry an oleo 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.
~here 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 ~or
generating such a plate described previously may be
summarized as follows: (1) coat the hydrophilic plate
surface with a thin layer of hydrophobic layer mater;al, (2)
select;vely remove the layer in the des;red con-f;gurat;on,
and, (3) as an optional step, coat the resulting plate wi-th
gum, the gum ordinar;ly adher;ng only to the exposed
port;ons of plate surface. Alternative processes for
generating the above described plate, as well as alternat;ve
pr;nting plate constructions, however, are possible.
The above plate comprising hydrophobic layer material
and gum in contiguous areas may be generated e;ther by
selective removal of a uniform layer of hydrophobic layer
material, followed by a gumm;ng step, as summarized above,
or, for example, by (l) cover;ng the plate surface w;th a
th;n layer of gum, (2) remov;ng select;vely port;ons of the
gum layer ;n a des;red configurat;on and (3) coat;ng the
resultlng plate w;th a hydrophob;c layer material. Many
hydrophob;c layer mater;als will not readily cover the
- 46 -
~L222~2
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
rnaterial and gum in contiguous 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, pre-determined 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
subst~tuted 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 -
~L~2~
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 confiyuring the hydrophobic layer material, as
before.
As suggested above, alternative plate constructions are
also possible. Where a durably-imaged plate is desiredl for
example, a suitable plate may be generated by (1) covering
the hydrophilic plate surface with a thin underlayer of gum,
(2) coatiny the gum underlayer with a thin overlayer of
hydrophobic layer material, and (3) selectively removing the
overlayer of hydrophobic layer material in the desired
configuration, without substantially disturbing the
underlying gum. Depending upon the choice of materials, it
has been founcl that application of the hydrophobic layer
material while in the vapor state, and allowing the material
to condense onto the gum surface, or heatlng the hydrophobic
layer material prior to application, aids in the formation
of the requisite hydrophobic overlayer recited in step (~).
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
~5 and tends to renlain intact compared with the hydrophobic
layer material, and the imaging energy may be readily
- 48 -
12Z2~
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, coated 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 overlayer 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 overlayer. 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 oleo ink is applied to a
plate surFace which has been selectively wetted, in
;
- 49 -
~2~Z~l~
image-complernentary 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 rnay 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 hydrophob;c, 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. This means that the electronic image
generating means which controls the selective application or
removal of the hydrophobic layer material must be modified
to lmpart 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 -
24~2
the latent image may be said to correlate with the resultingir,k ~mage, in that one either directly implies or is
complementary to the other.) The process of cleaning
âqueous ink from the roll may be somewhat clifferent than in
the oleo 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
]O situations where aqueous inks are advantageous.
Consideration of the alternative processes and plate
constructions, and use of aqueous rather than oleo inks, as
discussed above, does not change significantly either the
manner in which the various plates may be generated, imaged,
erased, re-imaged, 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
2n durably-imaged plate comprising a complete, specially gummed
underlayer and a configured overlayer of hydrophobic layer
material is to be generated and run without re-imaging 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
~ZiZ~lZ
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 gurn 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 oleo 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.
Re-imaging 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 aqeuous 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 re-imaging
subsystem 88. Re-application of a gum layer, if
- 52 -
~L2
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 re-imaging steps above~ as well as the
application of a fresh layer of hydrophobic layer material,
followed by re-imaging 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
confiyuration 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 o~ material to the interior sur~ace of the
desired cells. It should be noted that, preferably, the
material and application means are chosen to permit the
- 53 -
~IZ2Z~Z
application of a monomolecular or near-monomolecular layer
of the material which coats the walls and floor, or portions
thereof, of the desired cells and conforms thereto. It is
not necessary that 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 gravure 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 gravure 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 -
~;~224~Z
to a suitable substrate by conventional means, e.g., direct
cylinder-to-substrate contact. As discussed above, if an
oleo 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 gravure cylinder may be easily re-used~
i.e., re-imaged, 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 rnaterial from the cells. ~fter thus thorollghly
cleaning the cylinder of all dirt, coatings, etc., a fresh
quantity of hydrophobic layer material may be applied as
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 ind1vidual intra-cellular
area coated by the hydrophobic layer material, i.e., the
amount of interior cell surface which ls coated with a layer
of hydrophobic layer material within individual cells may
vary.
The various sequences of cleaning, imaging, printing,
re-imaging, etc., and the automated manner in which these
processes may be carried out, as discussed above in
- 55 -
~z~ z`
connection with planographic plates, are equally applicable
where a gravure roll is used, except for modifications which
will be apparent to those skilled in the art and which are
dictated by conventional gravure printing procedures.
A seamless cylindrical screen s;milar 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
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. Doctorin~
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 metering devices, such as a soft doctor blade, could be
used as well. Rolls 97, 99 serve to prevent deformation of
- 56 -
1;~22412
screen 92 9 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 Fiyure 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 is adsorbed on the wire mesh
in area 112~ and does not occlude the screen openings 114;
wire mesh outside area 110, as depicted at 116, 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 S0 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
I material may therefore be consideed substantially
¦ 25 non~occlusive.The aqueous ink is then transferred to a
substrate, as explained above. It is foreseen, however,
- 57 -
~I~ZZ412
that if a process resembling a conventional lithographic
process is desired, using a screen in place of a solid
lithographic plate, an oleo, lithographic-type ink may be
used, dlong with a suitable fountain solution or other
aqueous developer material. In this case, the oleo 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, configuraton, 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 mater;al, or after imaging, is opt;onal.
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 -
~2~12
employed as well, with appropriate modification to theimaging and printing methods and apparatus. The various
sequences of cleaning, imaging, printing, re-imaging, etc.,
and the automated manner in which these processes may be
carried out, as discussed above in connection with
planographic plates and gravure 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 -
~22~2
EXAMPLE I
A five mil (0.005 inch) thick plain stainless steel
sheet supplied by the Precision Steel Warehouse, Inc. of
~owners 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
ln 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 mils in diameter supplied by the California
Fine Wire Company, of Grover City, Callfornia, with an
adjacent wire spaciny of approximately one-half inch, was
positioned so that the distance between the wire tips and
the stainless steel sheet surface was approximately three
mils. 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 +~00 volt D.C. 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 -
:~Z2;~4~
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 o-f 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 Pantone
Process Brown ink, (supplied by A M Multigraphics, a
division of A M International, Mt. Prospect,Illinois). The
fountain solution used was a solution of one part (by
volurne) 3M Duplicator Fountain Concentrate, supplied by 3M
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 -
lZ~24~2
sheet surface. The fountain solution was observ~d 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 clid not accept ink. The
inked image was transferred to the blanket cylinder where it
was transferred to paper. A clean, sharp, well-defined
1n 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 uninked 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 -
EXAMPLE II
The procedures of Example I were followed, except as
noted below. A five mil 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
Multigraphics, Mt. 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
foulin~ 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 -
~2~4~L~
EXAMPLE III
A five mil thick plain stainless steel sheet supplied by
the Precision Steel Warehouse, Inc. of Downers Grove,
Illinois, w~s mounted on the plate cylinder of a Multilith
1250 Offset Lithographic Duplicator, made by A M
Interna-tional, of Los Angeles, California, in place of a
conventionally prepared lithographic plate. A linear array
comprising parallel tungsten wires 10 mils 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 w;re tips and
the plate was approximately three mils. 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 D.C. 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 stearate 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 O/S
H/T Process ~lue fifteen per cent 23401 ink, made by
Sinclair and Valentine Co., of Charlotte, North Carolina.
The fountain solution used was a solution of 31 parts (by
volume) water and one part (by volume) RBP Craftsman
- 64 -
~2~24~
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 approYimately four yards per minllte
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
duplicator frame. Argon gas was directed to the region of
the wlre 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 -
~Z;~2
The inked ima~e 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 recoated with the sodium stearate solution and
rinsed with distilled water, as before. T?he imaging and
printing processes described above were repeated. Again,
the result was a series of clean, sharp, well-defined ima~es
of uninked lines traced within a reg;on of solid ink,
similar to those obtained earlier. There was no visible
trace of the earlier image.
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:
~;~2~
EXAMPLE IV
The surface of a glass roll approximately 4 inches in
cliameter and comprised of 60,~.; Al203 and 40~0 TiO2 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 mil diameter tungsten stylus, spaced 2.0 mils
From the roll surface. An electrical current of 8 milliamps
at +800 volts was established in a spark discharge between
the roll and the stylus, as the roll turned at a
circumferential speed of 4.6 ypm, 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 atmospher;c pressure.
A mixture (by weight) of 1 part 3M Duplicator Fountain
Concentrate, clistributed by 3M Printing Products Division,
St. Paul, Minnesota, and 15 parts of distilled water, was
applied to the general area of the roll surfdce carrying the
image and allowed to remain momentarily. A roller was used
to apply an adclitional quantity of the above solution, which
was observed to wet only the ima~ed area. A
lithographic-type ink (Offset Black BI8261, manufactured by
Burntwood Industried, Inc., of Addison, Illinois) was then
applied to the general area of the roll surface carrying the
- 67 -
image via d roller. The ink adhered to the roll surface
only where the fountain so1ution had not wet the roll, i.e.,
in those areas which had not been imayed by the spark
discharge. The ink image was then transferred to paper. A
sharp, well-defined printed imaye was observed. Additional
quantities of fountain solution and ;nk 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.
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EXAMPLE V
A 4" x 1" section o-f five mil (0.005 inch) thick type
304 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
600F oven for one minute to ~/aporize any surface
contaminants which may have been present on the sheet
surface. The sheet was then dipped in a solution comprisin~
0.2 grams of hexadecanoic acid dissolved in a solù~ion of
100 ml dlstilled 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 yas and securely mounted on a grounded, steel
cylinder in order to image the sheet surface. A single
tungsten wire approximately 10 mils in diameter supplied by
the Cali-fornia Fine Wire Company, of Gro~er City,
California, was positioned so that the distance between the
wire tip and the stainless steel sheet surface was
approximately three mils. 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
D.C. power supply adiusted to deliver -~800 volt pulses at a
frequency of 17 KHz. 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 -
1;2224~
The stainless steel sheet was held at ground potentiat via
contact with the yrounded cylinder. Argon gas was directed
to the region of the wire t~ps, 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 3M Fountain Solution, distributed by 3M
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 3M R-Type
plate, distributed by 3M Printing Products DiYision, St.
Paul, Minnesota, which had been imayed previously with a
diagnostic pattern, thereby forming a "hybrid" plate. The
"hybrid" plate was then mounted in a Multilith 1250 Offset
Lithographic Duplicator (made by AM International, Los
2n Angeles, California) in place of a conventionally prepared
lithographic plate. The duplicator was inked with Pantone
Process Blue No. 530-8000, (supplied by AM Multigraphics, a
division of AM International, Mt. Prospect, Illinois). The
fountain solution used was a solut;on of one part (by
volume) Rosos Fountain Solution G-7A-~-Comb, supplied by
Rosos, Inc., Lake Bluff, Illinois, and 31 parts (by volume)
- 70 -
Z~Z
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 sùrface. The
fountain solution was observed to wet only those areas of
the stainless steel insert where the arc had impinged. The
ink, being imnliscible with the foun~ain solution, coated
only the remainder of the stainless steel insert containing
no fountain solution. The rest of the plate, i.e., the
conventional, d;agnostically 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 uninked 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 re-use, the stainless steel insert was
removed from the hybrid plate and cleaned by hand using
Blankrola , distributed by AM Multigraphics, of Mt.
Prospect, Illinois. After air drying, the insert was rinsed
with isopropyl alcohol and again air dried. The shim was
securely re-mounted on the grounded steel cylinder at
4 ~f9 A ~ ~
approximately a 45 angle to the direction of cyl;nder
rotation. The plate was imaged as before, except that a
voltage of +95U 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 ~ times over the
same area. The shim was then rinsed with palmitic acid and
gently rubbed with a paper tissue. Following this, the shim
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 for~n the "hybrid" plate as above,
and remounted on the above lithographic dupl;cator.
Multiple copies were printed which showed the same clean,
sharp ilnage as before, except that the original un;nked 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 re-image 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 re-imaged
as above, forminy 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
- 72 -
~'ZZ4~
was then re-inserted into the standard platel as before, and
mounted in the duplicator. Multiple copies were printed
which showed the same clean sharp image that was originally
visihle after the first arcing. The same uninked line,
corresponding to the area traced by the arc~ appeared but
without the Former ink containing area visible in the
previous print. In effect, this ared hdd been re-i~aged.
- 73
~2~2
EXA~IPLE V I
The procedures of Example V w~re repeated, except that
4" x 1" section of fi~e mil thick aluminum shim stock, from
the same supplier, was substituted for the stainless steel
shim, with similar results.
- 74 -
~Z2;~
EXA~iPLE VII
A 4" x 1" section of five mil thick type 304 stainless
steel sheet, supplied by the Precision Steel Warehouse, Inc.
of Do~ners Grove, ~llinois 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 of 4.6 yards per minute, the irnaging procedures of
Example IV were followed. 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
lO drops of TERAPRINT Blue R disperse dye, ~istributed by
Ciba Geigy Corporation, Greensboro, North 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. Re-application of the mixture to the sheet, and the
subsequent transfer to paper, yielded similar results.
- 75 -
~22Zg~Z
EXAMPLE VIII
A stainless steel sheet and a copper sheet, each 5 mils
thick and each supplied by Precision Steel Warehouse, Inc.,
of Downers Grove, Illinois, were separately illuminated by a
pulsed ruby laser manufactured hy Apollo Lasers, Inc. of Los
Angeles, California. The laser had an average beam energy
of 3.5 Joules, a heam cross-sectional area of appro~imately
0.0123 square inches, and a pulse width of 40 nonoseconds.
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, indicatiny that the hydrophobic
layer had been selectively removed in a pre-determined
configuration and a precise, well-defined
hydrophilic/hydrophobic image had been inscribed onto each
sheet.
- 76 -
~zz~
EXAMPLE IX
The procedure of E~ample VIII was repeated, using 5 mil
sheets of zinc and aluminum by Alfa Products of Danvers,
Massachusetts, in place of the stainless steel and copper
sheets. Similar results were obtained.
While specific componen-ts 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.
~ZZ~ L2
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 600F for
one minute to clean -the surface. The roll was then dipped
in the hexadecanoic acid solution of Example V and
im~ediately 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 kilohms. Four
short, evenly laterally spaced dashes were traced by the
spark. The roll was then squirted with an ink comprising
(by volume) 50% distilled water and 50~ Sheaffer Skrip blue
fountain pen ink, distributed by Sheaffer 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.
- 78 -
~Z~2~
~XAMPLE XI
A small section of stainless steel screen (120 x 108
mesh) supplied by McMaster-Carr, Inc., Elmhurst, Illinois,
~as 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 Exarnple IV were followed. The screen was made
wettable in the area traced by the spark. The ima~ed screen
was then dipped in distilled water to which a small quantity
of Pelikan Yellow drawin~ ink distributed by Pelikan AG,
Hannover, 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.
- 79 -
