U.S. patent number 3,800,699 [Application Number 05/337,124] was granted by the patent office on 1974-04-02 for fountain solution image apparatus for electronic lithography.
Invention is credited to Adam Loran Carley.
United States Patent |
3,800,699 |
Carley |
April 2, 1974 |
**Please see images for:
( Certificate of Correction ) ** |
FOUNTAIN SOLUTION IMAGE APPARATUS FOR ELECTRONIC LITHOGRAPHY
Abstract
A method and apparatus for printing an image in scanned
electronic form on an ink receiving surface using ordinary
printer's ink. The method and apparatus employ quasi-lithographic
techniques and equipment, but unlike conventional lithography, the
method does not require the preparation, prior to the printing
process, of a lithographic plate containing in permanent form the
image to be printed. The scanned electronic image is used to form a
fountain solution image on a lithographically blank plate by the
selective deposition and/or removal of the fountain solution from
the plate. Lithographic ink is applied to the fountain solution
imaged plate and then transferred to an ink receiving surface, such
as paper or an offset blanket. Thereafter, the lithographically
blank plate is cleaned and ready for the formation of the same or a
different fountain solution image. This is a division of
application Ser. No. 46,935, filed June 17, 1970, now U.S. Pat. No.
3,741,118.
Inventors: |
Carley; Adam Loran (Cambridge,
MA) |
Family
ID: |
26724453 |
Appl.
No.: |
05/337,124 |
Filed: |
March 1, 1973 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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46935 |
Jun 17, 1970 |
3741118 |
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Current U.S.
Class: |
101/147;
101/451 |
Current CPC
Class: |
B41M
1/06 (20130101); B41C 1/06 (20130101); B41C
1/1066 (20130101) |
Current International
Class: |
B41C
1/10 (20060101); B41C 1/00 (20060101); B41M
1/06 (20060101); B41M 1/00 (20060101); B41C
1/06 (20060101); B41l 025/12 (); B41l 025/06 () |
Field of
Search: |
;101/147,132.5,366,451,452 ;346/140 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Coughenour; Clyde I.
Attorney, Agent or Firm: Chittick, Thompson & Pfund
Claims
What I claim and desire to secure by Letters Patent of the United
States is:
1. Apparatus for applying a fountain solution image to a
lithographic plate comprising:
1. a printing head comprising:
a. means containing a vaporized or liquid fountain solution,
b. a plurality of spaced fountain solution dispensing passageways
fluidly coupled to said fountain solution containing means,
c. selectively energizable electrical means in each passageway for
supplying heat to the fountain solution passing through selected
dispensing passageways
2. means positioning a lithographic plate in pre-determined spaced
relation with respect to the dispensing passageways of said
printing head; and,
3. means producing relative movement between said lithographic
plate and said printing head.
Description
BACKGROUND OF THE INVENTION
The present invention relates to printing in general, and more
particularly, to a method and apparatus for electronic
printing.
The printing industry today utilizes a number of printing
techniques, the major types of which include lithography,
letterpress, and intaglio. Lithography is a technique which employs
a plate on which the areas corresponding to the inked section of
the image are hydrophobic, whereas the other areas are hydrophilic.
Neither area is significantly raised or indented with respect to
the other. An aqueous-based "fountain solution" is applied to the
plate. The fountain solution adheres to the hydrophilic areas only.
An oil-base ink is then applied to the plate. The ink is repelled
by the fountain solution and adheres only to the hydrophobic areas
of the plate. The lithographic plate is then brought into contact
with paper on which the ink image is printed (direct Lithography)
or with a resilient rubber blanket which in turn prints on paper
(offset lithography).
The second technique, letterpress, utilizes a plate on which areas
corresponding to the inked section of the image are raised. When
ink is applied to the plate, the ink adheres to the raised portions
only. When paper is brought into contact with the type (plate), the
ink adheres to it in the pattern of the raised portion. This
technique is currently used for printing many newspapers and
magazines.
The third major type of printing, intaglio, employs a plate on
which areas corresponding to the inked section of the image are
indented. When ink is applied to the plate, the ink remains in the
indented portions only. When paper is brought into contact with the
plate, the ink is absorbed by it in the pattern of the indented
portion.
The three major processes described above all require that a plate
be prepared prior to the printing process which contains in some
permanent form the image to be printed. In practice, such plates
are used on presses, repeatedly, so as rapidly to produce many
copies of the same original. However, it is not possible to
introduce a new original without interrupting the printing process
to change a plate. This is not only costly but time consuming.
Recent advances in technology have produced a number of other
"printing" techniques. Of interest are the various electro-static
processes including xerographic copying which uses techniques not
involving a permanent plate, but instead creates a charged pattern
on a photoconductor such as, zinc oxide or selenium to which a
powdered ink selectively adheres. The photoconductor is either on
an intermediary, e.g., drum, or the paper itself. In the latter
case, a costly and undesirable special paper is involved. In both
cases, the toner or electrostatic ink is much more expensive than
printer's ink, and in the former case, a fragile, costly and
gradually deteriorating photo conducting drum is required. In
general, the quality is noticeably inferior to printing and for
photographic work is unacceptable.
Photography or chemical imaging is a technique whose variations
involve light-sensitive chemical reactions, heat-sensitive chemical
reactions, possible intermediary images, developing reagents,
chemical image transfers, etc. The disadvantages of photographic
printing are that the per-print cost is high and the processes are
generally slow and inconvenient. However, quality is quite
high.
Other techniques include facsimile, thermal-wax transfer systems,
rupturable ink containing globules, and a wax vaporization transfer
process. The wax transfer process is illustrated in British Pat.
Nos. 943,401, 943,402 and 943,403.
All of the systems described above have certain advantages and
disadvantages. Generally speaking, when the reproduced image
quality is high, the cost per-print is correspondingly high and the
process may not have the desired speed. On the other hand, the
speed can be increased and cost reduced with concomitant sacrifice
in image quality.
It is accordingly, a general object of this present invention to
provide a method and apparatus for printing an image at high speeds
with high quality at a low cost.
It is a specific object of the invention to provide a method and
apparatus for printing a visible image from an image in scanned
electronic form.
It is another object of the invention to provide a method and
apparatus for printing which utilizes a number of conventional
lithographic printing techniques and lithographic equipment.
It is still another object of the invention to provide a method and
apparatus for printing which employs a re-usable image receiving
and transferring member.
It is a further object of the present invention to provide a
re-usable image receiving and transferring member which can receive
and transfer the same or different images.
BRIEF SUMMARY OF THE INVENTION
The present invention produces a copy which is similar to a
lithographically printed copy and uses many of the component parts
of a lithographic press, but eliminates the need for preparation
prior to the printing process of a plate containing the image to be
printed in permanent form. The image is supplied to the printing
unit in scanned electronic form, i.e., a television signal. The
signal can be generated either directly by electronic equipment
such as a computer or video tape, or by a camera using electronic
or mechanical scanning, with a without image storage and with a
scanned or unscanned light source.
The scanned electronic signal is used to form a "fountain solution"
image on a lithographically blank portion of a lithographic plate.
The term "lithographically blank," refers to a lithographic plate
which would print blank on an ordinary lithographic press. The
entire surface of the lithographically blank portion of the plate
is hydrophilic. A water or aqueous-based fountain solution image is
formed on electronically selected areas of the lithographically
blank portion of the plate. The fountain solution image corresponds
to the desired image, but in complementary form. The formation of
the fountain solution image is produced by the selective removal of
the fountain solution from the lithographically blank portion of
the lithographic plate or by the selective deposition of the
fountain solution on the lithographically blank portion.
The fountain-solution-imaged-plate is then exposed to a
lithographic ink which adheres only to the dry areas of the plate.
The ink forms an ink image which is a complement of the fountain
solution image. The inked plate image is then brought into contact
with an ink receiving means such as, for example, paper, tinfoil,
or an intermediary offset blanket. The excess ink subsequently
cleaned from the plate (and blanket, if used) by a cleaning
mechanism leaving the plate completely blank and dry.
Since no permanent lithographic image was formed on the plate, the
lithographically blank portions of the plate can be re-imaged with
a fountain solution and the process repeated as often as desired.
The re-imaging of the lithographic plate can be used to produce
multiple copies of a single original or copies of different
originals or electronically created images.
The objects and features of the present invention will best be
understood from a detailed description of the preferred embodiments
thereof, selected for purposes of illustration, and shown in the
accompanying drawings in which:
FIG. 1 is a block flow diagram illustrating the steps of the
printing process after conversion of the original into a scanned
electronic signal;
FIG. 2 is a diagrammatic view and partial schematic showing a
representative scanning and imaging system;
FIG. 3 is a sectional side view illustrating the application of a
fountain solution to the hydrophilic surface of the
lithographically blank plate;
FIG. 4 is a sectional side view illustrating the selective removal
of the fountain solution by vaporization produced by an intensity
modulated laser beam;
FIG. 5 is a sectional view depicting the application of ink to the
areas where the fountain solution has been selectively removed;
FIG. 6 is a sectional side view showing an ink receiving means,
such as paper, in contact with the wetted and inked surface of the
lithographic plate;
FIG. 7 is a sectional side view similar to FIG. 6 showing the ink
image on the ink receiving means after removal of the means from
contact with the lithographic plate;
FIG. 8 is a diagrammatic and sectional side view of a modified
lithographic press which simultaneously and repeatedly performs the
functions illustrated in FIGS. 3-7;
FIG. 9 is a sectional side view of an alternative embodiment
providing for the selective removal of the fountain solution by
means of an electrode;
FIG. 10 is a view similar to the view shown in FIG. 9 showing the
lithographic plate having a special surface in the form of a
checkerboard anodic coating;
FIG. 11 is a sectional side view illustrating the selective
deposition of the fountain solution on the lithographically blank
portion of the lithographic plate; and,
FIG. 12 is a view in partial block and diagrammatic form depicting
the printing head which is used to selectively deposit the fountain
solution on the lithographic plate.
Turning now to the drawings, and particularly to FIG. 1 thereof,
there is shown in block form a flow chart illustrating the steps of
the electronic lithographic process of the present invention. It
has already been mentioned that the image to be printed is supplied
in scanned electronic form to the printing unit, described below in
detail.
In general, the parameters of the scanned electronic signal, such
as frame-rate, number of lines, etc., differ markedly from a
standard television signal and the signal is non-interlaced. The
source of television signal does not comprise part of the
invention. The signal can be generated in a number of ways, either
directly by electronic equipment, such as a computer, or from
video-tape or by a camera using electronic or mechanical scanning,
with or without image storage, i.e., integration, and with a
scanned or unscanned light source. The color or black and white
camera can be an integral part of the printing unit or separate
from it. Conventional camera technology and electronic signal
generation and processing is employed and need not be described in
detail. It is sufficient to note that some of the currently
available camera techniques which can be employed to produce the
scanned electronic signal include: image orithicon, videcon,
flying-spot scanner, rotating mirrors, rotating prism, scanned
laser light source and dichroic mirror color separation. The
"television" or signal parameters are selected for the speed,
aspect ratio and resolution desired. Compared to standard 525 line
television signals, representative values for printing three 8 1/2
.times. 11 inch copies per second at 150-screen resolution are:
frame rate, one tenth; resolved elements, ten times; and bandwidth,
the same.
In the case of color printing, the colors in the original are
separated and matrixed electronically and, if desired, delayed, to
produce separate television signals for each color ink used in the
printing process. In addition, non-linearities in the printing
process may require gray-scale (gamma) correction in the television
signal before it is fed to the printing unit.
The scanned electronic image signal generated by any of the means
described above is used to form a fountain solution image on a
lithographic plate having at least a portion thereof which is
lithographically blank. A lithographically "blank" plate is a plate
which will print blank pages on an ordinary lithographic press. The
lithographically blank portion of the plate has a surface which is
entirely hydrophilic. A fountain solution is made to adhere to
electronically selected areas of the lithographically blank
lithographic plate in response to the scanned electrical signal
representing the desired image. As will be described in greater
detail below, the formation of the fountain solution image is done
by either depositing the fountain solution on selected areas of the
lithographically blank portion or by first coating the entire plate
with the fountain solution and then selectively removing some of
the fountain solution.
The term "fountain solution" refers to a liquid usually comprising
water, which renders a plate surface non-receptive to ink. The
terms "oil based ink," "hydrophilic plate," and "aqueous solution"
should be considered special cases of the functional terms
"lithographic ink," "lithographically blank plate," and "fountain
solution." In present lithographic practice, the fountain solution
comprises water plus various additives, notably alcohol. The
selective deposition or removal of the fountain solution is
obtained in the present invention by selective condensation or
vaporization. Therefore, only the volatile components (including
water) of the fountain solution will be imaged. The fountain
solution additives do not, per se, form a part of the invention and
it should be emphasized that pure water or even salt water will
work in the lithographic process.
The now fountain-solution-imaged lithographic plate is contacted
with a lithographic (e.g., oil-based) ink which adheres only to the
dry areas of the plate. The lithographic ink forms an ink image on
the plate which is the complement of the fountain solution image.
The application of the lithographic ink to the lithographic plate
is done by using conventional lithographic techniques and
equipment. The inked lithographic plate is then brought into
contact with an ink receiving means, such as paper or a
lithographic blanket. The ink is then transferred by contact onto
the paper either directly of via an intermediary blanket, onto
which the ink image is printed.
After cleaning, the lithographic plate is ready for another
fountain solution imaging process. It will be appreciated at this
point in the description of the invention that the lithographically
blank portion of the lithographic plate permits the repeated
formation of fountain solution images on the plate. The fountain
solution images can be the same or different depending upon the
type of printing desired. If multiple copies of a single image are
desired, the same fountain solution image will be formed on the
lithographic plate. On the other hand, if copies of different
images are required, then the fountain solution image will be
different for each different image.
The term "plate" as used herein should be construed broadly to
include planar as well as curved plates which can be either rigid
or resilient. In the case of offset lithography, the plate
preferably should be curved and rigid to facilitate use in
conventional lithographic presses. However, for direct lithography,
a resilient plate is preferred. Turing now to FIG. 2, there is
shown in diagrammatic and partial block diagram form a
representative system for obtaining the scanned electronic signal
and using the signal to form a fountain solution image on a
lithographically blank lithographic plate. An original 10
containing image information 12 is black-and-white, color,
gray-scale, and/or continuous tone is positioned for scanning
beneath a scanner 14. The scanning operation can be fully optical
with no movement of the original as indicated by the crossed arrows
16, or the original can be moved past the scanner by means of a
transport system 18 to provide vertical scanning. The scanner 14
produces an electronic signal representing the image information 12
on the original. This electronic signal can be used directly to
control the formation of a fountain solution image 20 on a
lithographically blank plate 22 or the electronic signal can be
processed to manipulate the image or stored for subsequent usage.
Manipulations include transmission, storage, collating, masking,
mixing, negative, contrast enhancement, color correction, and other
specialized alterations such as sequence numbering of printed
forms. The manipulations of the electronic signal are performed by
conventional and well-known signal processing circuits or computer
indicated by the reference numeral 24. The storage of the
electronic signal can be on tape, discs, and other conventional
signal storing means, all of which are indicated generally by the
reference numeral 26.
Given the scanned or otherwise generated electronic signal
representing the imaged original 10, in one embodiment of the
invention, the electronic signal is used to modulate the beam of
light emitted by a laser 28. The laser beam impinges upon the
lithographically blank lithographic plate 22 which has been
previously coated with a thin layer of a fountain solution. As the
laser beam scans across the fountain solution coated plate, the
fountain solution is vaporized from the plate to form the desired
fountain solution image. Horizontal scanning of the laser beam can
be provided by a number of conventional means including rapidly
rotating optics (not shown) which moves the laser beam across the
plate. The corresponding vertical scanning can also be accomplished
opto-mechanically, but the preferred method is to use the
mechanical motion provided by a suitable transport system indicated
generally in FIG. 2 by the reference numeral 30. In practice, the
mechanical motion of the lithographic plate on the lithographic
press can be used to provide the requisite vertical scanning of the
plate.
The scanned television signal modulates the laser beam by
modulating the intensity of the beam, the size of the light spot at
the plate or by varying the scan velocity of the beam. The energy
in the light spot is absorbed by the plate's surface which is
colored to absorb the laser light. The plate surface then supplies
heat-of-vaporization to the fountain solution which is in thermal
contact with it.
The scanned electronic signal produces a laser beam intensity or
spot size corresponding to the amount of ink desired at that point
in the image. With the laser "full on" all of the fountain solution
will be evaporated and a maximum amount of ink will be deposited on
the plate. The corresponding spot on the ink receiving means, e.g.,
paper, will be "black", i.e., inked. With the laser "full off" the
corresponding spot on the paper is left white because none of the
fountain solution was evaporated. A whole range of half-tones can
be achieved by in between modulation of the laser. For additional
fidelity, size modulated half-tone dots can be formed in the
horizontal dimension by means of a mode-locked laser or other
optical means. The image is differentiated in the vertical
dimension by the scanning lines.
The operation of the laser embodiment of the present invention can
best be understood by referring to the sequential steps illustrated
in FIGS. 3-7. The lithographically blank plate 22 whose top surface
32 is everywhere hydrophilic is coated with a fountain solution 34
by means of a dampener roller 36. The modulated laser beam laser 28
is depicted diagrammatically in FIG. 4 and identified by the
reference numeral 38. The beam selectively evaporates the fountain
solution 34 in the form of the desired image. After formation of
the fountain solution image by selective vaporization, the fountain
solution-imaged lithographic plate is coated with a lithographic
ink 40 by means of an ink form roller 42. The ink adheres only to
those areas where the fountain solution has been removed as shown
in FIG. 5.
FIG. 6 depicts an ink receiving means 44, such as a sheet of paper
or an offset blanket, in contact with the ink 40 and fountain
solution 34. FIG. 5 illustrates the paper or blanket 44 after it
has been removed from contact with the inked lithographic plate.
The ink 40 adheres to the ink receiving means 44 in the form of the
desired image. Some ink remains behind on the lithographic plate
while the fountain solution evaporates or is absorbed by the
paper.
FIG. 8 illustrates how the complete electronic lithographic process
can be performed on a repeating basis. The lithographic plate 22 is
mounted on a conventional plate cylinder 46. The fountain solution
34 is applied to the plate surface 32 in the manner of existing
lithographic presses. This is represented in a simplified form in
FIG. 8 by a fountain solution reservoir 48 which feeds the fountain
solution 34 onto a roller 50 which in turn applied the fountain
solution to the hydrophilic surface 32 of the lithographic plate
22.
The modulated laser beam 38 selectively removes the fountain
solution 34 to form the desired image. The lithographic ink 40
passes from an ink reservoir 52 onto an ink application form roller
54, again, illustrated in simplified form, and then onto the areas
of the plate surfaces 32 where the fountain solution was removed by
the laser beam. The ink receiving means 44, such as paper, is
pressed against the lithographic plate by means of an impression
cylinder 56. Some of the ink adheres to the paper, and the fountain
solution evaporates. The remainder of the ink is cleaned off the
plate surface 32 by means of a suitable cleaning system, one such
system, shown in simplified form comprises one or more rotary
cleaning brushes 58. A suitable cleaning solvent 60 passes from
reservoir 62 onto the cleaning brushes 58 to facilitate ink
removal. The cleaning solvent 60 and ink 40 are both removed from
the brushes by a solvent recirculation system 64.
The preceding description has referred to the use of a laser beam
to selectively evaporate the fountain solution from the desired
areas on the lithographically blank lithographic plate. It will be
appreciated while UV, visible or IR light can be used to vaporize
the fountain solution, visible light is preferred.
The process described in connection with FIG. 8 illustrates the use
of the present invention in direct lithography. In offset
lithography, a blanket cylinder (not shown) is positioned between
the plate cylinder 46 and the impression cylinder 56 with the ink
receiving means 44 passing between the impression cylinder and the
blanket. A cleaning system (not shown) is used to clean the
blanket.
The selective removal of the fountain solution to form a fountain
solution image on the lithographically blank lithographic plate can
be accomplished in a variety of ways. FIG. 9 depicts an alternative
method for selective removal of the fountain solution. Again, a
layer of fountain solution is first applied to the lithographic
plate and then selectively removed. In this case, a "head" 66 is
used to remove the fountain solution. The "head" 66 rides
hydroynamically/aerodynamically on the surface of the fountain
solution not touching the plate itself. The head 66 contains a
plurality of electrodes 68; one of which is shown in FIG. 9. A
separate electrode 68 is employed for each resolution element
across the horizontal dimension of the image.
The surface of the lithographic plate is made of conducting
material such as grained aluminum. An iterated circuit, such as a
shift register (not shown) applies the scanned electronic signal to
the electrodes and performs the horizontal de-scanning function.
The fountain solution is selectively vaporized by the ohmic heating
produced by electrical current flow through the solution. The
intensity of the current is varied according to the amount of
fountain solution to be removed, i.e., the amount of ink required
at each point.
A similar system is illustrated in FIG. 10 except that for the
surface 32 of the lithographic plate 22 is no longer made entirely
of a conducting material. Instead, it comprises an alternating
pattern of conducting and non-conducting material, 70 and 72
respectively, arranged in "checkerboard" fashion. The side of one
"square" on the "checkerboard" is less than one resolution element.
Such a surface can be prepared as follows. A standard
"checkerboard" printing screen (photographic negative) is
photographically reduced to the appropriate size. Using the
resulting reduced screen, photo-resist is applied to an aluminum
plate in the reduced "checkerboard" pattern. The plate is then
anodized; the photo-resist will insure that only the area not
covered by the photo-resist will be anodized. The photo-resist is
then removed with acetone. The resulting plate is selectively
anodized in a fine checkerboard pattern. The anodic coating is not
only an electrical insulator, but furthermore, it is also raised
above the aluminum itself. The head 66 moves over the plate
selectively evaporating the fountain solution by passing current
through the solution as described above. However, in this case, the
head 66 rides directly on the raised squares 72 of the anodic
coating, rather than hydrodynamically/aerodynamically on the
fountain solution itself.
Another variation in the geometry of the electrodes and
lithographic plate be accomplished by placing the electrodes in
electrical contact as well as physical contact with the plate. The
surface of the plate comprises an electrically resistive,
lithographic substance coated on a grounded conductor. The
necessary heat in generated in the surface of the plate as the
current passes into it. The fountain solution is in turn heated
selectively by thermal conduction from the underlying plate. Unlike
the examples discussed in connection with FIGS. 9 and 10, no
current is conducted by the fountain solution itself. In all these
configurations, the current can be applied in short pulses to
create vertical half-tone dots, while the horizontal dots are
created by the discrete nature of the electrodes.
Turning now to FIG. 11, there is shown a steam-water head version
of the present invention. The selective deposition of a fountain
solution on the lithographically blank lithographic plate can be
accomplished by converting the fountain solution into steam and
then condensing the steam on the selected areas of the lithographic
plate. Alternatively, water can be directly applied to the selected
areas. Looking at FIG. 12, the lithographic plate 22 starts out dry
and a long narrow head 66 applies water to it in the form of the
desired fountain solution image. The head 66 comprises an
electrical and thermal insulator 74, such as glass, containing a
row of tiny capillaries or passageways 76, one of which is shown in
FIG. 11. There is capillary or passageway 76 for each horizontal
resolution element. Preferably, the thickness of the insulator
substantially is the same as the depth of the capillaries 66 and
many times the capillary diameter. For purposes of illustration and
clarity the respective dimensions of the capillary diameter and the
thickness of the insulator have not been drawn to scale in FIG. 11.
The inside of each capillary 76 is plated with a thin-film
resistive material 78, such as metal. By means of tiny wires 80,
each capillary's plating is connected to an iterated electronic
circuit, such as a shift register 82. The shift register passes
current through the lining of the capillaries and performs the
horizontal de-scanning function. The vertical scanning function is
provided by the mechanical motion of the plate on the press. Here,
as before, the terms "horizontal" and "vertical" refer to
television terminology and not necessarily to the actual
orientation of the image.
On one side of the head 66 is a sealed vessel 84 containing
saturated steam and water at a fixed pressure above atmospheric.
The steam escapes through the capillaries and condenses on the
lithographic plate to form the fountain solution image. The steam
is replenished by a servo-mechanism (not shown) which applies heat
to the water in the vessel. The steam discharging end of each
capillary is positioned very close to, but not necessarily
touching, the rapidly moving lithographic plate. Before
encountering the head 66, the dry lithographic plate is at a known
temperature below 100.degree. C.
A current passing through each capillary lining 78 generates heat
according to the scanned television signal, as sampled for that
capillary. The heat is carried away by the high velocity steam,
increasing its temperature. Two effects cause the amount of steam
hitting the plate to be less the hotter the steam temperature.
First the steam's viscosity increases with temperature causing the
volume passing through the capillary to decrease. Second, the steam
expands causing the mass for a given volume to decrease. The
combined effect is, very roughly, a T.sup.-.sup.2 temperature
dependence. By this mechanism, the amount of steam condensing on
the "black" image areas is substantially less than on "white" image
areas. The temperature of the lithographic plate is selected to
just barely re-evaporate all the water from the purest black areas,
leaving varying amounts in other areas. This re-evaporation takes
place between the steam head and the ink form roller (not shown in
FIG. 11). A third effect at this point, augments the viscosity and
gas-law effects: in the darker areas the hottor steam releases more
heat on condensing and thereby promotes the re-evaporation in those
areas.
Instead of using steam, cold water can be passed through the
capillaries 76 and be selectively heated by the electric current
passing through the capillary lining 78. Hotter water, having a
markedly lower viscosity will flow more freely than the cold water.
The viscosity of the water is 1.79 at freezing; 1.00 at room
temperature, and 0.28 at boiling (centipoise) with a continuous
range in between. The density change is slight. Flow in a capillary
is inverse to viscosity giving a flow range of 6.2 to 1, which is
roughly the same as obtainable for the previously described steam
system. The water is applied to the plate either by spraying it on,
vaporizing it and spraying it on, or "wiping" it on. The capillary
employed is much, e.g., tenfold, smaller than for the steam
situation.
Another variation for the head configuration shown in FIG. 11 is to
pass hot water through the capillary 76 and selectively vaporize
the water by heat. The steam will constrict the flow because of its
radically lower density, in spite of its lower viscosity. The term
"hot" refers to water temperature near 100.degree.C. The steam
produced is also near 100.degree.C. The viscosity of the water at
100.degree.C is 0.2828cp, for steam 0.125, a ratio of 22 to 1
favoring steam by volume. However, the densities (at 100.degree.C)
favor water by 1600 to 1, or a net of 70 to 1 more flow for water.
The advantages of utilizing the hot water system for selectively
forming the fountain solution image include: constant temperature,
no signal heat loss, no thermal time delay in the capillary, much
less signal heat required, excellent extinction ratio (70 to 1) and
no need for "re-evaporation" from the plate.
Referring now to FIG. 12, there is shown in diagrammatic and
partial block form the previously described printing head 66 and
the major associated electronic circuitry. For purposes of
illustration, the printing head 66 is shown in FIG. 12 with
capillaries 76. However, it should be understood that the electrode
version of the head described in connection with FIGS. 9 and 10 can
be substituted, in which case a dampener system is used.
Printing head 66 is positioned over a plate transport system,
indicated representationally by a moving web 86. The
lithographically blank lithographic plate 22 is carried by the web
86 beneath the printing head thereby providing vertical scanning of
the image. Horizontal scanning of the image is obtained by
sequentially energizing the capillaires 76 (or electrodes) in
response to the scanned electronic signal representing the desired
image.
It will be appreciated that the present invention permits the
formation of the fountain solution image 20, either by selective
removal or deposition of the fountain solution, directly from an
electrical representation of the fountain solution image without
any intermediary image means. This situation is illustrated in FIG.
12 by the direct connection of a computer 88 to the printing head
66. Of course, it is also possible to work from an original image
by converting the original image into a scanned electronic signal
by means of a suitable scanner 14, as previously described. Again,
no intermediary image is required between the television signal and
the fountain solution image.
After formation of the fountain solution image 20 by selective
deposition or removal, the fountain solution imaged lithographic
plate passes to an inking station as indicated by the arrow in FIG.
12. In practice, it is desirable to structure printing and inking
stations to conform to conventional lithographic equipment.
Therefor, looking back at FIG. 8, the printing head 66 is
positioned at and substituted for the laser beam 38. With this
configuration, multiple copies of the same image (either an
original image or an electronic, e.g., computer generated image)
can be produced rapidly and inexpensively. Single copies also can
be produced from different images, either originals or
electronically generated. Furthermore, with multiple printing heads
and inking stations, multiple colors, including black, can be
printed on the same ink receiving means.
The present invention lends itself to repetitive printing jobs in
which one or more informational elements are changed in each print.
For instance, "form letters" have the same body material but
different addresses. The "body" of the letter preferably is
permanently formed on a lithographic plate in the conventional
manner. However, the addressee portion of the plate is
lithographically blank so that a separate and different fountain
solution image can be formed for each addressee. It is also
possible, but not as desirable, to form the entire letter including
the body and addressee each time by the selective fountain solution
deposition or removal techniques of the present invention.
Having described in detail a number of embodiments of the
invention, it will be appreciated that various modifications can be
employed to achieve the desired selective deposition and/or removal
of the fountain solution form the lithographically blank portion of
the lithographic plate. For example, intense non-laser light can be
used to vaporize the fountain solution in response to an electronic
signal representing the desired image.
Other modifications can also be used, such as various types of
fountain solutions, including non-aqueous solutions which can be
selectively deposited or removed from a lithographically blank
lithographic plate.
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