U.S. patent number 3,752,073 [Application Number 05/137,688] was granted by the patent office on 1973-08-14 for process for single-impression multicolor printing.
This patent grant is currently assigned to Bernard Olcott. Invention is credited to Leslie H. Lorber.
United States Patent |
3,752,073 |
Lorber |
August 14, 1973 |
PROCESS FOR SINGLE-IMPRESSION MULTICOLOR PRINTING
Abstract
Process of producing an apparent full color print of a
multicolored picture, comprising the steps of: A. by use of a
composite separation screen having interspersed 1st and 2nd filter
areas which transmit substantially red and substantially green
information, respectively, of the multicolored picture,
photomechanically forming upon a printing surface halftone printing
elements of a composite image having correspondingly interspersed
1st and 2nd information areas respectively for the red and the
green information, all of the halftone printing elements being
receptive to a dark ink of substantially neutral tone; B.
photomechanically forming field printing elements upon the printing
surface only in portions of the surface corresponding to the 1st
information areas, the field printing elements providing background
to the halftone printing elements occurring within the 1st
information areas, the field printing elements being receptive to a
substantially red ink; C. inking the halftone printing elements
with the dark ink and the field printing elements with the red ink;
and D. simultaneously transferring the inks upon the printing
elements to a receiving substrate of a selected pale color.
Inventors: |
Lorber; Leslie H. (Boston,
MA) |
Assignee: |
Olcott; Bernard (Atlantic
Highlands, NJ)
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Family
ID: |
22478627 |
Appl.
No.: |
05/137,688 |
Filed: |
April 26, 1971 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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754168 |
Aug 20, 1968 |
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Current U.S.
Class: |
101/211;
101/401.1; 101/450.1; 430/301 |
Current CPC
Class: |
G03G
5/12 (20130101); G03F 3/04 (20130101); G03G
13/01 (20130101); B41M 1/20 (20130101) |
Current International
Class: |
B41M
1/20 (20060101); B41M 1/14 (20060101); G03G
13/01 (20060101); G03G 5/12 (20060101); G03F
3/04 (20060101); G03F 3/00 (20060101); B41m
001/20 (); B41m 003/00 () |
Field of
Search: |
;101/450-452,211,426,175,176,395-401.1 ;96/30-32 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
"Multicolor Effects on Two-Color Presses", Dupont Magazine,
Sept.-Oct. 1968, Vol. 62, No. 5, pages 2-5, E. I. Dupont de
Nemours, Wilmington, Del..
|
Primary Examiner: Fisher; J. Reed
Parent Case Text
This application is a divisional application of my earlier filed
copending application, Ser. No. 754,168, now abandoned, filed Aug.
20, 1968.
Claims
What I claim is:
1. Process of producing an apparent full color print of a
multicolored picture, comprising the following steps:
a. by use of a composite separation screen having inter-spersed 1st
and 2nd filter areas which transmit substantially red and
substantially green information, respectively, of said multicolored
picture, photomechanically forming upon a printing surface halftone
printing elements of a composite image having correspondingly
interspersed 1st and 2nd information areas respectively for said
red and said green information, all said halftone printing elements
being receptive to a dark ink of substantially neutral tone;
b. photomechanically forming field printing elements upon said
printing surface only in portions of said surface corresponding to
said 1st information areas, said field printing elements providing
background to said halftone printing elements occurring within said
1st information areas, said field printing elements being receptive
to a substantially red ink;
c. inking said halftone printing elements with said dark ink and
said field printing elements with said red ink; and
d. simultaneously transferring inks upon said printing elements to
a receiving substrate of selected pale color.
2. Process according to claim 1 wherein said 1st and 2nd inks are
mutually immiscible,
3. Process according to claim 1 wherein said 1st ink is black, said
2nd ink is bright red, and said receiving surface is white.
4. Process according to claim 1 wherein said 1st ink is blue-black,
said 2nd ink is bright red, and said receiving surface is greenish
white.
5. Process according to claim 1 wherein said printing plate has
text printing areas, and said text printing areas receive said 1st
ink together with said 1st and 2nd plate images.
Description
My invention relates to the single-impression printing of
multicolor pictures. Certain disclosures are also applicable to
color projections and other optical color displays.
In Scientific American, May 1959, Dr. Edwin H. Land describes
apparent colors whose perception is independent of the classical
additive primaries. For example, an unexpected range of natural
colors can be perceived merely by the use of red and white or two
yellows, and black. By "natural" it is meant that the apparent
colors are properly located in a picture and substantially correct
in value and chroma. The article deals with projected and otherwise
optically displayed pictures, but Land has also applied his
findings to the printed page. I shall hereinafter refer to pictures
such as Land describes and related phenomena as being
"non-Maxwellian," inasmuch as they are at least in part distinct
from the classical experiments of James Clerk Maxwell.
According to the existing art, a non-Maxwellian print requires
either: (a) Two image-bearing plates to be printed in accurate
register upon paper, either the paper or the illuminant or both
preferably being of bluish tint (Land, U.S. Pat. No. 3,034,890); or
(b) Accurate press register between a plurality of image-bearing
plates, and use of an especially prepared single colored or
multicolored patterned receiving surface (Land, U.S. Pat. Nos.
3,003,391 and 3,147,699). In his patents Land does not refer to his
Scientific American article, but among his various embodiments are
those clearly relating to phenomena described in the cited issue of
Scientific American.
A principal object of my invention is to disclose means to print a
natural multicolor picture in a single impression upon white or
light-tinted paper and other plain surfaces.
Another object is to provide plates that will print a natural
multicolor picture with but two inks, in one impression.
Still another object is to allow the single-impression printing of
a natural multicolor picture simultaneously with other graphics,
such as type matter, line work and halftones.
Yet another object is to permit incidental graphics accompanying a
natural multicolor picture printed in one impression to be of dark
tone and/or a particular color.
A further object is to provide for single-impression printing of
natural multicolor pictures by means which eliminate color
misregister on the press, which are adapted to high-speed rotary
letterpress and planographic equipment (modified), which can
utilize either an original or duplicate plate, and which are
simple, economic and versatile.
Still a further object is to disclose means to enhance the fullness
of gamut elicited by non-Maxwellian prints and optical displays;
and
Yet a further object is to minimize the need for a tinted paper or
tinted illuminant in non-Maxwellian prints and optical displays,
respectively, or the depth of tint when such paper or illuminant is
used.
Specific means to this invention and other objects thereof will
become known from the accompanying drawings, which are enlarged,
schematic and not necessarily to scale, wherein:
FIG. 1 shows a corner of a piece of paper upon which an apparently
natural multicolor picture has been printed;
FIG. 2 shows a corner of a photographic composite image which can
be used to prepare my printing plate;
FIG. 3 depicts a means of direct compositing/halftoning;
FIG. 4 shows the essential character of a "compositing screen";
FIG. 4a shows a possible section through the screen of FIG. 4,
taken at the plane a--a;
FIG. 5 shows a corner of a plate which may have been used to print
the picture shown in FIG. 1;
FIG. 5a shows a possible section through the plate of FIG. 5a,
taken at the plane a--a;
FIG. 6 depicts an indirect means of forming a halftone composite
image;
FIGS. 7 through 10 show stages in producing some types of my relief
plate;
FIG. 11 shows a female mold which may be used to form duplicates of
my relief plates;
FIGS. 12 through 16 show some types of my duplicate relief
plate;
FIG. 17 shows stages in producing my "common" lithographic
plate;
FIG. 18 shows stages in producing my "deep-etch" lithographic
plate;
FIG. 19 shows stages in preparing my "magnetic" plate;
FIG. 20 shows stages in preparing a xerographic surface for
printing a natural multicolor picture in a single transfer;
FIG. 21 shows stages in the preparation of my "electrostatic"
plate;
FIG. 22 shows the suggested net response of a preferred short
separation;
FIG. 23 shows the suggested net response of a preferred long
separation;
FIG. 24 depicts specially-prepared positive transparencies for
projecting a non-Maxwellian picture of improved gamut; and
FIG. 25 shows a "single-impression duotone" plate.
Broadly, and with exceptions, the means of my invention comprise:
(a) Obtaining a photographic halftone image which is a composite of
two selected color separations; (b) Utilizing the photographic
composite to prepare a printing plate bearing a corresponding
positive image; (c) Forming "field printers" on the plate
contiguous to halftone dots of one particular component of the
composite; (d) Utilizing plate materials and constructions that
permit selective receptivity of inks or fluids generally applied
across the whole plate surface; (e) Inking the plate with
appropriate inks, which allows the composite image to accept ink of
a "dark" tone and the "field printers" to accept ink of a selected
color; and (f) Making a direct or offset impression onto paper or
another receiving surface which, if not white, is of a selected
tint or fuller color.
The "field printers" do not contain or print pictorial information,
i.e., they comprise no "image" in the usual sense. Expressions
involving the word "image" such as "composite image," "plate
image," "ink image" refer only to that part of the plate or
complete reproduction having pictorial content. The word "print"
used as a noun refers to the reproduction as a whole. Numerals 12,
13 refer to a photographic image; notation 12', 13' refers to the
plate image; and notation 12", 12" refers to the printed image.
Subscripts may be used for other forms of a composite image.
THE COMPLETE REPRODUCTION
A complete print, depicted shematically in FIG. 1, comprises a
positive halftone composite image 12", 13" printed in a "dark" ink
upon paper or another contrasting receiving surface 14. For clarity
the halftone dots 12" and 13" are greatly enlarged and few in
number, and no attempt has been made to actually represent a
picture. The "dark" ink may be neutral or achromatic in tone, e.g.,
black or a value of gray as taught by Land, but preferably it is
partially chromatic as described herein under the subject "Gamut
Enhancement."
The printed composite image 12", 13" is accompanied by fields 10 of
a selected color, e.g., a red, that are printed by "field printers"
of the plate simultaneously with the image. These color fields 10
function as one of the two "stimuli" necessary for non-Maxwellian
effects.
Receiving surface 14 may be white, tinted or of fuller hue. A
feature of this invention is that surface 14 may more suitably be
white or a very pale tint than has herebefore been wholly
satisfactory for non-Maxwellian prints. Intervals of surface 14
between the color fields, where not occluded by halftone dots 13",
function as the other of the two "stimuli" necessary for
non-Maxwellian effects.
For best results the tint or fuller hue of the receiving surface is
selected according to recommendations later given in the section
"Gamut Enhancement," as is the specific color of the [color]
fields. However, satisfactory results will be obtained when these
"stimuli" are selected according to Land's teaching.
Color fields 10 are ordinarily distributed throughout the picture,
but as an option they may be made absent from all or some highlight
portions of the picture in addition to or in lieu of the absence of
highlight halftone dots. Surprisingly, local absence of color
fields is unnecessary for apparently true whites to be perceived
(even if the receiving surface is tinted or of fuller hue).
When a print such as described and made as recommended is viewed in
common illuminants or by daylight, a natural multicolor picture is
perceived. Because all pictorial information resides in the "dark"
image, because there is no desaturation due to physical color
admixture as in "process" prints, and because there can be no loss
of sharpness due to press misregister, the reproductions will have
a crisp, bright quality rivaling reproductions made by conventional
means. Also because the composite image contains all pictorial
information and detail, the image strongly arrests the attention
away from the composite pattern and color fields, which elements
can be surprisingly large without becoming overtly noticeable as
would coarse halftone dots.
THE COMPOSITE IMAGE
To form my printing plate I may first obtain a photographic
composite image. As shown in FIG. 2, this may comprise halftone
dots 12 of a "long" color separation image and halftone dots 13 of
a "short" color separation image upon a film 9, of black-and-white
nature. The "long" and "short" separations in their original
negative form may, on black-and-white film, respectively record
long-wavelength and short-wavelength colors of the original subject
or copy, as described by Land. (A "short" separation can
permissibly be an ordinary panchromatic image obtained without use
of a filter; in claims where two color separations are mentioned,
the use of such a panchromatic "separation" is within the intended
scope.) The separations preferably have further characteristics
disclosed herein under the subject "Gamut Enhancement." The
photographic halftone composite image 12, 13 is assumed to be in
positive form so that its correspondence to the printed image may
more readily be seen. However, a photographic halftone composite
image in negative form may be used when required for plate
expsoure. A halftone composite image substitutes for the
conventional platemaker's halftone image, and is used in an
equivalent manner thereto.
Wherever I may mention or depict film, reference is actually to the
emulsion on said film, and instead of a film support glass plate or
equivalents may be used. While my photographs, as conventional in
platemaking, are ordinarily black-and-white, it will be understood
that the white (clear) portions may be dyed and that such a dyed
image may nevertheless be equivalently used in forming an image
upon a sensitized printing plate.
In further particulars, component areas L and S, respectively
corresponding to portions of the long and short separations, are
arranged in a sufficiently fine interlace or mosaic so that to
casual inspection the two partial images appear as one. The two
separations are, in effect, in interspersed register. [The
composite pattern is quite satisfactorily coarser than the halftone
screen.] While each component area L and S is shown as being of a
size which will accommodate several halftone dots as they might
more or less randomly fall, this is purely exemplary. Each
component area might, in practice, be of a size which will
accommodate one halftone dot or but part of a halftone dot. If
desired, the halftone screen might be designed to locate each dot
particularly with respect to component areas, e.g., central
thereto.
A halftone screen may have the same angle for both separations, or
may be differently angled for each. The angle(s) should be selected
as to avoid moire effects with the color fields that will be
present in the complete reproduction. For convenience in
representation halftone dots 12 and 13 are shown as they may fall
with single angling. An advantage of differential angling is that a
composite so-made may be printed on rougher material with less
apparent quality loss, than could a single-angled composite of
equivalent screen fineness. Halftone dots 12 are shown as being
different in size from dots 13, indicative of tonal differences
ordinarily occurring between separations; dots 12 are arbitrarily
shown as being larger. In practice, halftone dots will not all be
of circular shape, and may abut and cojoin with one another, and
might solidly occupy individual component areas in shadow portions
of the picture.
A mosaic of rectangular areas L and S has been chosen to facilitate
understanding. However, any other composite pattern of order 2 may
be used, for example: parallel strips; wavy strips; concentric
rings; triangular mosaics; irregular mosaics; circles or other
configurations on a field (the field comprising one component and
the configurations the other component). A preferred pattern is one
that is in general regular, substantially nondirectional, and such
that the two separations occupy roughly equal amounts of total
picture area. As will later be understood, deliberate inequality of
the total area of each separation may be introduced as a means of
adjusting color balance, although other means are preferred and
will be described.
I may obtain a halftone composite on film by the direct means shown
in FIG. 3. It is assumed that platemaking requires a negative. The
face of a "compositing screen" 3 is placed in intimate contact with
the emulsion of panchromatic film 9, preferably of high contrast.
Compositing screen 3, here represented schematically, may actually
be as shown in FIG. 4 comprising transparent polarized areas 1 and
2. Areas 1 and 2, respectively, positionally correspond to
components L and S of the composite shown in FIG. 2. Areas 1 are
polarized in one direction and areas 2 are polarized in a
substantially opposite direction. As may be seen in section in FIG.
4a, polarized areas 1 and 2 may be formed as topical elements of
polarized material, e.g., molecularly aligned dichroically stained
polyvinyl alcohol, or a matrix containing aligned dichroic
crystals, upon a support 3' of glass or other transparent,
preferably stable, material. Various other obvious constructions
may be used, but concern here is for the optical characteristics of
the screen.
A halftone screen 4, e.g., of the crossline type, is placed at
"screen distance" in front of the film. This screen may be angled
so as to avoid moire effects with the composite pattern. A first
exposure to color copy 11 is then made through a long separation
filter 5 and through a polarizing filter 6 oriented to polarize
light so that it will only pass through correspondingly polarized
screen areas, e.g., areas 1. Thus halftone dots 12 which represent
the long separation will image on the film only behind areas 1, the
image being atten-uated by areas 2. A second exposure is then made
through a short separation filter 7 and through a polarizing filter
8 oriented to polarize light so that it will only pass through
compositing screen areas 2. (Polarizing filter 8 may be polarizing
filter 6 which has been rotated 90.degree. in its plane.) This
exposure images short record dots 13 behind compositing screen
areas 2. The halftone composite thus obtained is free of any
halftone dots which may incurse or protrude out of their proper
composite areas, as reflected by the "clippped" appearance of
certain dots. Incursion would distort tonal values to the detriment
of colors perceived in the final reproduction. As mentioned
previously, the halftone screen 4 may be angled differently for
each exposure, this being optional. The two angles in such case
would be selected to avoid moire effects with each other and with
the composite pattern.
By another direct means also with reference to FIG. 3, I may
substitute for polarized screen areas 1 and 2 colors corresponding
to the desired separation filters. No independent separation
filters 5 and 7 will then be required, nor will polarized filters 6
and 8 be needed. If areas 1 and 2 (which act as separation filters)
have either substantially equal filter factors or a deliberate
inequality in filter factor, only one exposure to color copy need
be made. If there is an undesired difference in filter factor an
appropriate compensating filter can be inserted into the optical
path during part or all of the exposure, or separation filters 5
and 7 can be used as before for two exposures. Assuming that the
respective colors of areas 1 and 2 are somewhat overlapping in
transmission as is generally desired for separation filters, a
certain amount of halftone dot incursion will occur. However, the
incursion in this case will be substantially "correct," as the
incursing portions of the dots will be partially attenuated and
reduced in size proportionate to the degree of transmission overlap
of the separation filters.
By indirect means shown in FIG. 6, I first obtain a desired pair of
long and short separations L and S which have been halftoned. These
may be in positive form. By successive exposures I first image one
halftone separation and then the other upon film 9. The film in
this case may be ordinary blue-sensitive film, and a polarized
compositing screen 3 as before described is against the film. For
each exposure a polarized filter 6 or 8 is respectively used,
essentially as before described for direct compositing. If desired,
separation L can have been given a different halftone screen angle
than separation S. The halftone screen angle(s) should, as before,
be selected to avoid moire effects. By this means a negative
platemaker's composite is obtained which is wholly free of halftone
dot incursion.
In a variation of the above indirect means, compositing screen
areas 1 and 2 are of mutually-exclusive colors, e.g., a near blue
and a far blue with no overlapping transmission. The use of two
blues will permit ordinary film to be used. If one of the
mutually-exclusive colors is green orthochromatic film must be
used; if one of the colors is red panchromatic film must be used.
Two exposures are made, but instead of polarized filters 6 and 8 a
pair of color filters is used. One color filter must be such that
light transmitted through it will only pass through screen areas 1,
and the other color filter must be such that its transmitted light
will only pass through screen areas 2. While the color filters must
generally correspond in color to their respective compositing
screen areas, exact correspondence is not required. Either the
screen areas and/or the color filters can be mutually-exclusive.
This means will result in a halftone composite image wholly free of
dot incursion.
In the various above-mentioned compositing means, where successive
exposures have been mentioned, the sequence may be reversed;
alternatively, a reverse beam splitter may be incorporated into the
optical system to allow simultaneous exposure of both separations
onto the film 9. I do not limit the general practice of this
invention to a halftone composite derived by the aforementioned
means, providing the composite has the essential structure as
described. Instead of dots halftone elements may be of a linear
form, as when the halftone screen is of a parallel ruled type or
the like; in such cases the composite areas L and S may also be
linear. Generally, the use of a dot-type halftone structure is
preferred.
In distinction to the halftoning means I have described a
continous-tone composite image may subsequently be halftoned, but
the resultant halftone composite will suffer from incorrect
incursion that will distort colors in the final reproduction.
Although such effects can be minimized by using a halftone screen
which is very fine relative to the composite pattern, and/or by
reducing shadow values, such corrective measures have obvious
practical shortcomings. I am fully aware that halftoning is not
always a last step in photographic procedures prior to platemaking,
and that direct halftoning from color copy is sometimes practiced.
Yet I believe that the application of such halftoning techniques in
conjunction with a compositing screen, for obtaining halftone
composites free of incorrect incursion, were never practiced and
remain unobvious a priori.
The use of a photographic composite for platemaking is merely a
convenience, and I may directly substitute for film a suitably
sensitized printing plate. As will be later understood, a
compositing screen can also be used as a "light-stencil" for
platemaking.
THE PLATE
A printing plate bearing a composite image may be as shown in FIG.
5 and in section in FIG. 5a. The composite plate image 12', 13' is
accompanied by "field printers" 20. The field printers may be
coincident with either long or short image components depending on
whether they are to be inked with a "warm" color or a "cool" color
ink. The drawing shows the field printers 20 associated with long
comonents and halftone dots 12' respective thereto, as this
particular association is preferred. For the section, the halftone
dots have been slightly re-arranged to facilitate schematic
representation. In this example the plate image 12', 13' is formed
wholly in relief in a body material 15. The field printers 20 are
also in relief, but have their printing surfaces flush with the
faces of the halftone dots; in effect, the field printers are in
planographic relationship to halftone dots 13' respective thereto.
The plate is shown in an un-inked state, but as will become
understood, halftone printing elements 12', 13' exclusively receive
an ink of "dark" tone and field printers 20 exclusively receive an
ink of selected color.
A plate that prints a complete reproduction in a single impression
may be in relief (non-printing portions being recessed) or it may
be planographic (printing and non-printing elements being nominally
in the same plane). Within these two broad classes a plate may have
various basic forms or "types" which may in turn have secondary
variations. The plate of FIG. 5 and FIG. 5a was shown mostly for
purposes of introductory description and is but one of several
embodiments hereinafter described. All other plate sections in
their final form may be considered alternative sections a--a of
FIG. 5. With few exceptions the plates are shown un-inked.
My relief plates will be described first as they generally
respresent the simplest means of practicing this invention,
although requiring more extensive description. Each type has
particular obvious advantages and no order of preference is
intended.
In the following descriptions, and throughout this specification,
any material not described as being hydrophilic is to be considered
grease-receptive or lipidophilic and also hydrophobic.
"Hydrophobic" is not used in an absolute sense, but means that a
material or surface is either poorly wettable or non-wettable by
water or other "wet" fluids as later described. A hydrophilic
material or surface is readily wetted by water and other "wet"
fluids.
RELIEF PLATE, TYPE I (FIG. 7d and FIGS. 5 and 5a). This plate is
characterized by having the composite image 12', 13' formed wholly
in relief in a body 15. Then the field printers 20 are formed
thereon of another material. Referring to FIG. 7a-d:
a. A positive halftone composite image 12', 13' is formed in relief
in a body 15. Any suitable means of formation may be used. For
example: the relief may be an original etched engraving in metal; a
molded or electrotype duplicate of an original engraving; a relief
formed on a photo-electric halftone engraving machine.
b. "Fill" 16 is applied to all recesses of the relief image. The
fill is applied nominally flush with the faces of the image or with
topping 17 thereupon. Fill may be inorganic, e.g., metal or
ceramic, or it may be organic, e.g., a natural or synthetic
polymer. Inorganic fill and organic fill which is not or cannot be
directly photosensitized may be coated with photoresist, as the
fill must be selectively removable by photoforming means. As here
assumed the fill is directly sensitized and organic, the
sensitization being of the "negative" light-insolublized type. As
also assumed, the fill is of a hydrophilic nature and remains
hydrophilic even after it has been light-reacted, or can be
re-rendered hydrophilic. Some such materials will be described
later. Topping 17, if used, may optionally be the resist used in
etching the plate. Topping provides an expedient means to form the
field printers 20 in slight (planographic) relief t relative to the
face of the plate image. Preferably the amount of relief t and the
corresponding thickness of topping 17 does not exceed roughly
two-thirds the face dimension of a highlight halftone dot. The use
of a slight amount of relief t is generally recommended, but is not
necessary except for certain purposes as will later be
understood.
c. Fill 16 (or photoresist thereon) where coincident with long
components of the composite and contiguous to halftone elements 12'
respective thereto, is exposed to actinic light through a
light-stencil 18. The light-stencil may comprise transparent areas
18a and opaque areas 18b on a transparent support 32, or may be as
later described and equivalent to a compositing screen.
d. Portions of fill 16 not reacted by the actinic light (or not
protected by light-reacted photoresist) are removed, e.g., by
solvent development. Topping 17, if any was used, may be removed by
solvent or reagent or other means non-destructive to remaining
portions of fill. Suitable topping may be left on the plate as an
ink-base for a lipid ink, and if necessary may be solvated or
softened. The image 12', 13', with or without topping, will receive
a lipid ink of "dark" tone. The residual fill 16' forms the field
printers 20, which if not already hydrophilic are treated to render
them so, and receive an aqueous or "wet" ink of selected color.
By variations in procedure and/or materials the relief image may be
or be rendered hydrophilic to receive an aqueous or "wet" ink of
"dark" tone, while the field printers receive a lipid ink of
selected color.
RELIEF PLATE, TYPE II (FIG. 8f). This plate is characterized by
being formed partly as a lithographic plate, e.g., halftone
elements 12' and field printers 20, and partly as a relief plate,
e.g., halftone elements 13'. (It is considered to be a relief plate
because non-printing portions are recessed.) Referring to FIG.
8a-f:
a. Positive halftone composite image 12', 13' is topically formed
on a plate 19. The plate may be a lithographic metal with a grained
surface 19'. The image is in slight relief t perferably not
exceeding roughly two-thirds the face dimension of a highlight
halftone dot. The typical image may be metal such as copper, brass
or zinc which has been electrolytically deposited through a
negative stencil after light counteretching (in the general manner
of a so-called "deep etch" lithographic plate but wherein metal has
been applied rather than ink-base). Photosensitized gum arabic may
suitably be used to form the stencil. The image may be rubbed up
with a hydrophobic and grease-receptive ink-base and/or etch resist
prior to removal of the stencil.
b. Bare areas of grained surface 19' are coated with a photoresist
21, e.g., of the "negative" light-insolublized type, preferably of
hydrophilic nature. Photoresist 21 may be applied flush with or in
slight excess of the image.
c. Photoresist 21, where coincident with long components of the
composite and contiguous to halftone dots 12' respective thereto,
is exposed to actinic light through a light-stencil 18, essentially
as before described with reference to a Type I relief plate.
d. Unexposed portions of photoresist 21 are removed, e.g., by
solvent development.
e. Bared areas of grained surface 19' are etched in depth, e.g., by
acid or electrolytic removal. The depth is sufficient so that
recessed portions of the plate image will not print (about 3 mils
for highlight regions of a 133-line halftone, taken as a
reference).
f. Residual resist 21' is removed, e.g., by solvent or reagent. The
solvent or reagent preferably does not dissolve or remove ink-base
or resist which has been applied to the image 12', 13'. The
underlying grained surface 19' forms the field printers 20, which
because of the graining are receptive to an aqueous or "wet" ink.
The "wet" ink applied to the field printers will be of a selected
color, while the lipid ink applied to the plate image will be of a
"dark" tone.
Instead of the plate image being of metal it may be of
light-reacted photoresist; instead of a grained surface 19' a
hydrophilic surface may be obtained by de-oxiding or chromate
treatment of the base metal, by formation of a sodium silicate film
thereon, and by other known means. In the case of a silicate
treatment initially uniform upon the plate, and when a metal image
12', 13' is used, the silicate film may be locally removed by light
abrasive blasting rather than chemical etching, to permit good
adherence of the metal image to the base metal.
By variations in procedure and/or materials, the plate image 12',
13' may be hydrophilic, e.g., by virtue of silicate treatment, and
the field printers 20 may be lipidophilic, e.g., by being formed of
a resinous hydrophobic resist.
RELIEF PLATE, TYPE III (FIG. 9c). This type of plate is
characterized by having the composite image 12', 13' and the field
printers 20 formed of the same material differentially treated.
Referring to FIG. 9a-c:
a. A latent positive halftone composite image 12, 13 is optically
formed in depth in a photosensitized hydrophilic organic material
23, e.g., sensitized gelatine, which material is preferably on a
stable support 22. Material or layer 23 is at least thick enough to
accommodate highlight dots of the relief image which will later be
formed in part for halftone elements 13 (about 3 mils for a
133-line halftone, taken as a reference). The exposure may best be
made by contact printing through a negative halftone composite
12.sub.n, 13.sub.n on a film 9, using slightly divergent light
rays. A full exposure is made to assure the maximum degree of
insolubility, as the exposed portions must be receptive to a lipid
or greasy ink.
b. Photolayer 23, where coincident with long components of the
composite and contiguous to latent halftone dots 12 respective
thereto, is exposed to actinic light through a light-stencil 18.
The stencil may be as before described with reference to a Type I
relief plate. The exposure is best made by contact printing, with
the rays of light slightly divergent. This exposure is partial,
sufficient to enable selective removal only of totally unexposed
portions of the photolayer, sufficient to prevent ready solubility
of partially exposed portions 24 when they are wetted by an aqueous
or "wet" ink, yet not so much as to cause a total loss of the
hydrophilic property of portions 24.
c. The plate is solvent or wash-off developed sufficiently to only
remove totally unexposed portions of photolayer 23. Partially
exposed portions 24 form the field printers 20 which receive an
aqueous or "wet" ink of selected color, and fully exposed portions
12,13 become the plate image 12',13' which receives a lipid ink of
"dark" tone.
It will be noted that image elements 12' are in true planographic
relationship with field printers 20. This is optional. To obtain a
slight relative relief t (as shown in other drawings) I may
counterremove part of the field printers after they have first been
formed flush, e.g., by etching or by fluid erosion, so they are in
slight intaglio relative to the plate image. (As will be
understood, when slight relative relief t is desired either the
field printers or the composite image may be in relief relative to
the other.) While it is convenient to utilize the same material for
the composite image and the field printers I do not limit myself to
such practice. After the composite image is optically formed and
developed into high relief, I may employ a wholly different
material to form the field printers.
RELIEF PLATE, TYPE IV (FIG. 10d). This plate is characterized by
having preformed field printers 20 in relief on or integral with a
support or body 26. The composite image 12',13' is subsequently
formed thereon, partly in relief (dots 13') and partly planographic
(dots 12'). It is deemed obvious from the drawing and from prior
descriptions how the composite image may be formed of
photosensitized material. Therefore the procedures here given will
relate to a bi-metallic embodiment. Referring to FIG. 10a-d:
a. Obtain a starting material. The starting material may comprise a
body 26 having preformed appended or integral relief elements 25
which will become the field printers 20 (FIG. 7d). The relief
elements 25 either are metal or are plated with a thin metal layer
27, as here shown. A metal layer 27 may also be applied to relief
elements of a different metal. Hereinafter in referring to relief
elements 25 it should be understood that said reference includes
any plating 27 thereon.
Relief elements 25 have a height nominally equal to the maximum
depth of the composite relief image that will later be formed
(roughly 3 mils for a 133-line halftone, taken as a reference), and
they are, in plan, of such shape and distribution as will enable
them to coincide with long components of the composite image.
Upon this structure is provided a flat-surfaced metal layer 28
which is of a metal selectively removable relative to underlying
material. Thus, assuming the use of a mild acid etchant or
electrolytic removal, layer 28 can, for example, be magnesium or
zinc and layer 27 may be copper, silver or gold or other less
electrolytically active metal. (The plate substructure can be
re-usable.) Layer 28 is in slight excess t above relief elements
25. The excess t preferably does not exceed roughly two-thirds the
face dimension of a highlight halftone dot of the intended
composite image.
Photoresist 29 is applied to layer 28. Sensitization of this resist
may suitably be of the "negative" light-insolublized type, and the
resist is preferably of hydrophilic nature. Before application of
the resist 29 the surface of layer 28 is rendered hydrophilic,
e.g., by formation of a sodium silicate film 30 thereon.
This starting material may be a ready-made manufactured product
(possibly with a sensitized topping 29) intended for use with a
composite image of standardized pattern.
b. By use of a photographic halftone composite instead of a usual
platemaker's halftone, a positive halftone composite image 12.sub.r
,13.sub.r is formed of light-reacted resist 29, and unexposed
portions are removed, e.g., by solvent development. The resist
image 12.sub.r,13.sub. r must be in accurate register with the
relief elements 25 so that long components of the composite image
and halftone dots 12.sub.r respective thereto are coincident with
elements 25. Because elements 25 are not visible, various indirect
means must be used to secure such register. For example, the excess
t of layer 28 could be locally removed beyond the actual picture
format of the plate. The exposed elements 25 can then be visually
aligned with a corresponding reference beyond the actual picture
format of the photographic composite image. Alternatively, resist
topping 29 may have a non-imaging, e.g., light blue, pattern
printed thereon which corresponds to the underlying pattern of
relief elements.
c. The resist image 12.sub.r,13.sub.r is formed in its various
degrees of relief, e.g., by abrasive blasting, chemical etching,
electrolytic removal or by combinations of such means. Halftone
dots 13.sub.r in particular must be eteched to their full depth so
that bottom printing will not occur from recesses therebetween.
d. Resist image 12.sub.r,13.sub.r is removed by a suitable reagent
or solvent; corresponding underlying faces of layer 28 thereby
become the composite plate image 12',13'. Relief elements 25
function as the field printers 20, where not occluded by halftone
dots 13'. Unlike other embodiments of relief plate that have been
described at length, in this case the image 12',13' is hydrophilic
and will receive a "wet" ink of "dark" tone, and field printers 20
will receive a lipid ink of selected color. By means that will be
understood from a general discussion later given, the field
printers 20 may be rendered hydrophilic instead of the plate
image.
In a variation, layer 28 is not originally formed in slight excess
t, but is flush with the faces of relief elements 25, the
photoresist 29 being commonly applied to both the layer 28 and the
relief elements. The resist image 12.sub.r,13.sub.4 is left on the
plate to directly become the plate image 12' ,13', etching taking
place only around dots 13.sub.r. The plate image 12',13' receives a
lipid ink of "dark" tone. Field printers 20, which are the parts of
relief elements 25 not occluded by halftone dots 12', must be or be
rendered hydrophilic and receptive to an aqueous or "wet" ink of
selected color.
GENERAL CONSIDERATIONS
As might already be understood from the description of my relief
plates, two immiscible inks are used-- one being lipid, and the
other aqueous or "wet". While I explain my invention in terms of a
lipid ink and a "wet" ink, I do not exclude the use of other
pigmented or dyed fluids which ae immiscible each with the other.
Preferably the lipid ink is the "dark" ink and the wet ink is the
color ink. Accordingly, in all the examples of plate construction
except for a Type IV plate, the field printers are ordinarily shown
and described as intended for receiving the wet ink.
By "wet" ink I mean any colored or toned fluid behaving essentially
as water relative to a lipid or greasy fluid, e.g., an aqueous
solution or suspension whether thin or mucilaginous, a low
viscosity polyvinyl alcohol, a simple alcohol solution or
suspension, or combinations of such fluids. By "alcohol" or "simple
alcohol" I mean to include methyl, ethyl, propyl or butyl alcohol,
isopropyl alcohol and isobutyl alcohols, and mixtures of these with
each other or with water. It will be understood that a wet ink will
be non-reducable or miscible with a solvent or thinner for the
lipid or greasy ink.
By "lipid" ink I intend to include greasy or hydrophobic resinous
ink such as is common to lithography and letterpress, whose vehicle
is reducable in an aromatic or aliphatic hydrocarbon solvent, and
any other colored or toned fluid substantially insoluble or
immiscible in water and/or alcohol. Those lipid inks most readily
soluble in the aromatic hydrocarbon solvents are generally
preferred. The term "lipid" is not solely intended to relate to
oleoaginous substances, but is here meant to include hydrophobic
polymers and resins in a fluid state.
To permit selective reception of the two inks, two different plate
materials are ordinarily used, but as will later be understood from
a discussion of duplicate plates, the two plate materials may be
exactly identical whether formed separately or at the same time,
yet may be selectively inked. Ordinarily though, one material is or
can be rendered hydrophilic and readily wettable, while the other
material is hydrophobic and but poorly wettable. Reference to
wetting solely relates to wetting by water and the like, unless
specifically stated otherwise. In nature, hydrophobic materials are
grease-receptive of lipidophilic. Therefore, unless otherwise
stated, a lipidophilic surface or material is also assumed to be
hydrophobic.
As was mentioned, the term "hydrophobic" is not used in an absolute
sense. Virtually all platemaking metals, natural resins and
synthetic polymers, and surface films natural thereto, e.g., common
oxide films, are adequately hydrophobic, and receptive to lipid
inks in the letterpress and lithographic consistencies herefor
employed. Thus elements intended to receive lipid ink and resist
wetting will require no special selection or surface treatment. It
is nevertheless desirable to apply a lipid ink-base to such
surfaces during an appropriate stage of plate preparation,
essentially as conventional, to further promote their receptivity
to lipid ink and rejection of wet ink.
Somewhat more care must be exercised in selecting materials to
receive the wet ink. While I rely much upon general knowledge in
the platemaking arts as to the various surface properties of
materials and means to enhance their wettability, some means of
enabling wettability will be reviewed here.
It is known that metals may be rendered hydrophilic by abrading,
graining, de-oxiding and formation of a hydrophilic silicate film
thereon. The amphoteric metals are most amenable to the latter
treatment, which may suitably be as described by Jewett, U.S. Pat.
No. 2,714,066. However, I do not limit treatments to flat surfaces
or sheet stock as is conventional, but may treat my plates in any
appropriate stage of their completion. Rubber and many other
elastomers may be rendered hydrophilic by oxide removal such as by
chromic acid, mild abrasion or a reducing flame, but are often
sufficiently hydrophilic for use herein even without such
treatment. Gelatine, casein, gum arabic, hydrolyzed cellulose
esters, hydrolyzed shellac, polyvinyl alcohol and other organic
materials are known to be hydrophilic, and by various known means
these materials may be mixed with each other and compounded and
mixed with different substances to give them further properties
desired in plate materials, e.g., insolubility without loss of
wettability, durability, etc. Instead of being limited to thin,
perhaps monomolecular, films of hydrophilic silicates, I may employ
such materials in thick section for plate elements. I may also form
hydrophilic plate elements of a light-reacted photosensitized
hydrolyzed organic ester, e.g., of cellulose acetate, which, after
formation is surface re-hydrolyzed to restore its wettability. Such
surface re-hydrolyzation has never been practiced in platemaking,
to the best of my knowledge. Alternatively, I may but partially
expose a photosensitized organic hydrophil, as was described in the
examples, so that it remains wettable. By a further alternative I
may form hydrophilic plate elements of a photosensitized hydrophil
which remains wettable after a full exposure, contrary to most such
materials. Photosensitive materials with such properties are
described by Oster, U.S. Pat. No. 3,097,096 column 7, line 53. In
the claims where a plate material or element has hydrophilic
surface character, or is topical and hydrophilic, I am concerned
solely with surface properties regardless of underlying structure
however thick or thin, which underlying structure may or may not
also be hydrophilic.
In discussing plate materials or elements I am specifically
concerned with those materials or elements which receive ink,
whether lipid or wet, and not with non-participating materials or
elements that may be employed as a support or for strength, or to
build up the plate in overall thickness. While I have shown at
least one material for each type of relief plate as being metal
(except for a Type III plate), I do not limit myself to such
practice. Plate materials will vary in their suitability for
various modes of printing. Metal is preferred for each of the two
plate materials when durability is especially important, as in
direct printing. Rubber and other elastomers may suitably be used
for both plate elements for printing on rough and inelastic
materials such as glass and sheet metal. For offset printing, use
of a photosensitized light-reacted organic material for one of the
plate elements, regardless of the other plate material, is suitable
for printing runs of average length and simplifies plate
preparation, and for offset printing duplicate plates later
described are also adequately suited as regards durability. As will
later be described, field printers may be formed (on a Type I
plate) of materials which do not have to be capable of selective
removal whether by photoforming or other means, some such materials
being platable metals, amalgams, ceramics and non-photosensitized
organics; the latter three categories can include materials which
are naturally hydrophilic without special treatment.
Although the use of a mucilaginous or somewhat thickened wet ink is
within the scope of this invention, the wet ink should in general
be as thin a fluid as possible without losing its ability to
film-wet the plate surfaces receiving it. Film-wetting is necessary
to keep a wet ink from running into the image recesses of a relief
plate and from being thrown off the plate at high printing speeds.
Film-wetting need not be absolute--a wet ink may permissibly have a
slight tendency to creep provided it remains substantially as a
film for the short duration until the plate has been impressed. The
more hydrophilic the plate material, the less mucilaginous and
tacky need be the wet ink. Thus, by using a suitably mucilaginous
wet ink many metals and polymeric materials not usually considered
to be hydrophilic may nevertheless be used to receive a wet ink. A
mucilaginous wet ink can also be used when a gloss or semi-gloss is
desired on the printed page. The term "mucilaginous" is herein used
as a description of tackiness or viscosity, and does not
necessarily imply that the mucilage be constituted of vegetable
gums or heteropolysaccharides as is common. For example I may use
as a mucilaginous ink a colored or dark toned viscous solution of
sodium or potassium silicate (water glass), or I may add such
material to another wet ink. Casein and other proteinous materials
in aqueous suspension are readily formulable in viscous
consistencies, and with appropriate coloring or toning may be used
as a wet ink of mucilaginous consistency or thinner consistency.
Heretofore to my knowledge, relief printing with wet inks has, as
in flexography, been limited to use of slow-oxidizing organic
materials such as rubber or of rubber-like nature, excluding metals
and other directly etchable or formable materials. I contemplate
making conventional relief plates of metal and other materials
which may not be especially hydrophilic and inking them with a
mucilaginous wet ink. As will later be understood, such plates may
be used in conjunction with my single-impression multicolor plates.
Of course I may also form such conventional reliefs of more readily
hydrophilic material, e.g., gelatine or soft rubber, as is known,
and apply a wet ink whether thin or mucilaginous thereto, and I may
also use such plates in conjunction with my single-impression
multicolor plates. When such conventional but wettable relief
plates are used alone the wet ink may be very thick and tacky, but
a wet ink cannot be excessively thick or mucilaginous for the
present single-impression multicolor plates as it will lose its
immiscibility with the lipid ink. However absolute immiscibility is
not required.
When the plate material for the wet ink is but poorly wettable and
a relatively thick mucilaginous ink is indicated, immiscibility
with the lipid ink may be enhanced by using dye rather than pigment
for one or both inks. The lipid ink in such case can advantageously
have suspended particles of wax or solid silicone polymer. This
will help it remain immiscible with the mucilaginous wet ink, by
making the lipid ink more stiff and waxy. As conventional the wax
additive may be dissolved, but the use of a solid wax additive is
preferred. Whenever two dyes are used, it is desirable that one be
an acid dye and the other be a basic dye, and that these be
mordanted to their respective fluids. (I consider two or more dyes
acting subtractively, and in the same fluid, to be equivalent to a
single dye.)
The lipid ink ordinarily has substantially greater body or
viscosity than the wet ink, being in the nature of letterpress ink
or at least of lithographic ink. It is within the scope of this
invention to use a reversed system wherein the lipid ink is thin
and the wet ink very thick, but such practice is not preferred. In
the latter mode of printing it is preferably the lipid ink which is
colored and the wet ink which is "dark." With either mode of inking
a slight amount of bleeding of the color ink is permissible on the
paper or other receiving surface. Such bleeding can create a
vignetted effect that will soften the apparent contrast of the
color fields against the background of paper. This will not be
detrimental to the crispness of the print if slight, as all the
detail and pictorial information is in the "dark" composite image.
Vignetted color fields may be slightly larger than would otherwise
be satisfactory. Emphasis is again made that the color fields may
be in general surprisingly large without being casually discernable
in the incomplete reproduction, e.g., they may be of the order of
32 per linear inch, interspersed by portions of the paper.
The reason why a lipid ink of letterpress consistency can be used
with an aqueous or like fluid for purposes of this invention,
whereas a reduced consistency lipid ink is conventionally used in
lithography in conjunction with an aqueous fountain or dampening
solution, is that the aqueous fluid is herein intended to print and
transfer to the paper. The wet fluid or ink may therefore be
applied somewhat more liberally than can the wetting solution used
in lithography. If, with the sparse wetting common to lithography a
more full-bodied lipid ink was employed, the lipid ink would tend
to take to the non-printing areas of the plate. Single color
lithography or monotone is not done with a thick lipid ink and more
generous water although such practice might thus seem feasible,
because so much of the average plate is non-printing that the total
amount of water carried to the paper would be excessive. With this
invention only a small percentage of the picture is printed in a
wet ink, and what moisture is transferred and might cause paper
distortion can be ignored because no subsequent impressions are
necessary. When a lipid ink of lithographic consistency is employed
for my plates the wet ink is preferably not at all or but slightly
mucilaginous, and the plate material therefor is preferably highly
hydrophilic. A thin wet ink may suitably be merely dyed alcohol
and/or water. Modern dyes are sufficiently intense so that only
sparse inking with the wet ink will be needed.
It should be understood that I do not limit hydrophilic surfaces
only to the reception of a wet ink whether thin or mucilaginous, as
such surfaces if dry can suitably receive a lipid ink. This fact
will be appreciated from a later discussion of duplicate plates
some of which depend thereon for their operation.
As particularly regards a Type I relief plate, various kinds of
fill which may be used can be applied to recesses of the plate
image by any means appropriate to its nature. Photosensitized and
non-sensitized organic fill may be originally in liquid, paste or
plastic form which is poured, rolled or wiped on. It can then be
doctored flush with the plate image or topping thereon while fluid,
or scraped flush after it has set. The actual photosensitization
may be done before or after application. Thermoplastic materials
may be melted on and then doctored flush, and similar procedure may
be used for low melting alloys. Platable metals may be
electrodeposited, any excess being mechanically removed as by
surface planing. Where a fill applied in solvated form may "sink"
due to loss of solvent by evaporation, the application may be
repeated as necessary to secure a flush surface, or the fill may be
applied in excess and allowed to dry, after which it is finished
flush. Photosensitized fill materials applied as a liquid need not
necessarily have set prior to exposure under a light-stencil. Some
such materials that may be exposed while in the liquid state are
described by Oster, U.S. Pat. Nos. 2,875,047; 3,074,794 and
3,097,096 and these are also sensitive to visible light and have
certain advantages both as fill and as photoresist which will later
be discussed. As was mentioned, Oster also describes hydrophilic
resists which remain hydrophilic after a full exposure. Materials
that may not be readily receptive to hydrophilic fill in liquified
or semi-liquid form may be made adequately receptive by phosphate
or chromate treatment or by other known means commonly employed
when depositing hydrophilic photoresists upon metal plates and
other supports of generally hydrophobic poorly-wettable nature.
Fill materials that cannot be directly photosensitized may, as
described, coated with photoresist and selectively removed by
photomechanical means. Alternative to such procedure these
materials when desired as field printers may be formed as follows:
First a directly sensitized fill is applied and is exposed under a
reverse or "negative" light-stencil wherein areas 18b are
transparent and areas 18a are opaque, except if the sensitization
of the fill is of the reversal or light-detached type. In the
latter case the usual light-stencil can be used. Unexposed or
light-detached portions of fill are then removed. The residual
portions of fill are used as a stencil for the application of the
desired non-sensitized fill fill which forms the field printers
after the stencil has been removed. Some materials suitable for
field printers formed by the aforementioned means include platable
metals, amalgams, sodium silicate grout, lime and other hydraulic
cements, and natural and synthetic polymers. Thus, field printers
may be formed which may be of material that does not have to be
selectively removable relative to the plate image, and which can be
naturally hydrophilic for reception of a wet ink, if the latter
property is desired.
For all relief plates and for other plates later described,
whenever a light-stencil is required it will be equivalent to use a
compositing screen, and especially advantageous when the
compositing screen is the very same as was originally used to form
the composite image. Accurate register between the image and the
field printers will thus be more readily assured. When a
compositing screen is substituted for a light-stencil only one set
of screen areas is caused to be attenuating to the actinic light,
these areas corresponding to light-stencil areas 18b in function.
For this purpose either a polarized filter or a color filter is
inserted into the optical path, depending on the particular type of
compositing screen. Use of a color compositing screen as a
light-stencil will also require that the photosensitive material on
the plate be responsive to the color of light transmitted by the
screen. Most photosensitized materials are blue sensitive;
obviously such materials will not be usable when the actinic light
is otherwise colored. For the latter case, Oster's photosensitive
materials are particularly useful.
If it is desired that color fields not be present in the highlight
portions of a complete print, their corresponding field printers
may either be kept from formation or locally removed from the
finished plate Local removal is most readily performed on a Type I
PLATE, E.G., by use of selective etchants or reagents. "Removal"
need not be complete, it being sufficient merely to reduce the
field printers below a printing height, and a vignetted effect is
readily achieved. Field printers may be locally kept from formation
by painting out on the light-stencil or equivalent. As was
mentioned, local absence of color fields is surprisingly
unnecessary for apparently true whites to be perceived.
DUPLICATE RELIEF PLATES
The relief plates hereinbefore described may be used to prepare
duplicates which will have an identical composite image and pattern
of field printers, although differing in structure. It is necessary
for such purpose to use an original plate which has a slight amount
of relief t. As was mentioned, either the field printers or the
plate image may be in relief t relative to the other although the
former is preferred. In all cases the relief t is sufficiently
slight as to maintain a nominal planographic relationship between
field printers and halftone dots respective thereto. Within this
limitation, the amount of relief should be as generous as is
possible. When an original plate is intended expressly for the
purpose of being used as a master for making duplicates, the plate
materials need not be selected with particular consideration as to
their working properties, and might only be suited for proof
inking. The materials of construction can be selected for their
ability to withstand the rigors of moldmaking. An original plate
that contains hardenable material, e.g., a partially exposed
organic resist, may, after running proofs, have such material
further hardened by appropriate physical or chemical means.
Original plates containing frail or elastomeric material not
ordinarily suited for use as a pattern in moldmaking, may have
duplicates made therefrom by means here described instead of more
conventional moldmaking procedures.
In general, an original relief plate of my construction may be
considered equivalent to an ordinary relief in the sense that
non-printing portions are recessed (and only in said sense). Any
conventional duplicating method may therefore be employed which
involves the making of a female mold from the original or master
and then obtaining one or more positive male duplicates therefrom.
Similar techniques may thus be used as are employed in making
electrotypes, stereotypes, plastiplates, "duplicate originals" and
rubber plates. As will be seen, my duplicates may be formed of many
conventional materials as well as many less common materials.
However, to my knowledge, conventional moldmaking methods involve
subjecting the original to considerable heat and/or pressure. Thus,
such means cannot be well-used on those of my original plates which
may contain frail or elastomeric or thermoplastic material, or
which are in other words "fragile." As shown in FIG. 11, for
duplicating fragile originals I prefer that the female mold 31
comprise a metal shell 32 which is electroformed upon the original.
When the shell 32 has reached a desired thickness it may be backed
up with any suitable rigid or semi-rigid material 33 for strength,
e.g., with epoxy resin or a cold-set plastic. This female mold is
then used to make either electrotype duplicates or cast or molded
duplicates.
Duplicates obtained from molds of my original relief plates will
differ from ordinary duplicate reliefs. My duplicates are,
regardless of an essentially homogeneous structure as first formed,
amenable to selective inking or treatment of only certain printing
surfaces. The various basic types of duplicate now described do not
relate to the "types" of original relief plates but are a distinct
notation. Each type has its own obvious advantages and no special
order of preference is intended.
DUPLICATE RELIEF PLATE, TYPE I (FIG. 12). This duplicate is molded
of naturally hydrophilic material 40. The material 40 must set firm
and still be hydrophilic, and must not be dissolved by wet ink at
ordinary operating temperatures. Among suitable organic materials
are hydrolyzed gelatine, hydrolyzed cellulosics, hydrolyzed casein,
hydrolyzed shellac, rubber, vinyl and acrylic latexes and soft
rubber; among inorganic materials are sodium and potassium
silicates, hydrocal plaster and lime cement. Hydrophilic organics,
in particular, may be compounded or admixed with other materials,
partially polymerized and otherwise rendered less readily soluble
and more durable. I do not limit this type of duplicate only to
organic and inorganic hydrophils in their most simple or common
forms. For my wet ink I may use simple water and/or alcohol dye
solutions or I may employ another wet ink related thereto, e.g., a
mucilaginous ink, casein ink, shellac ink, or a water-dispersed
latex. Pre-press preparation may be as follows:
When the freshly molded duplicate is dry, water or another thin wet
fluid is applied only to the slightly raised field printers 20.
This may be done by impressing the duplicate upon a wetted platen
or other flat surface. The fluid film on the platen must be
shallow, and the platen stiff, as the degree of relief t is very
slight. If necessary, repeated light impressions, slightly
displaced, may be made to assure full coverage of the field
printers and no other portions of the duplicate. Before the wet
fluid has dried the composite image 12',13' is conventionally
rolled up with lipid ink-base. The wetted field printers will
reject the lipid ink-base. By alternative procedure, first a lipid
ink-base is applied only to the field printers 20. Subsequently the
plate is rolled up with a wet fluid to which the ink-base is
repellant.
In the aforementioned preparatory procedures one or both fluids may
be colored or toned, and could be the actual inks used in the
press.
DUPLICATE RELIEF PLATE, TYPE II (FIG. 13). This duplicate has a
metal facing, preferably of an amphoteric metal such as magnesium
or aluminum. The facing 36 may be electrolytically deposited upon a
molded body; conversely, the duplicate may comprise an
electroformed facing or shell 36 to which a backing has been
applied. Regardless of how the duplicate body 37 is formed, the
metal facing or shell 36 is subsequently given a topical treatment
to render it hydrophilic, such means having been previously
reviewed. The treated layer of the facing 36 may be very thin,
perhaps monomolecular in the case of a silicate film, and is not
separately shown in the drawing because the exaggeration necessary
would make this duplicate difficult to compare with other
duplicates and original plates.
Although the whole metal facing is treated including the recesses,
by a variation only the faces of the field printers 20 can be
treated. This may be done by lightly impressing the metal-faced
duplicate against a platen or the like which has been sparsely
wetted with treating solution or abrasive, repeated slightly
displaced impressions or mild rubbing being used as required.
The molded body or backing 37 may be of any material commonly used
for such purposes, e.g., polyvinyl chloride, a phenolic resin or
any other suitably structural material to which a metal facing may
be firmly applied or which will adhere well to a metal shell.
Ordinarily it is irrelevant whether the backing is hydrophobic or
hydrophilic.
Pre-press preparation may be essentially as described for a
duplicate, Type I. However, if only field printers 20 were given a
hydrophilic treatment, after the duplicate is dry the first-applied
fluid should be wet.
By a variation in construction, after the whole facing including
the recesses has been given hydrophilic treatment, the facing may
be locally removed from the faces of the field printers. This will
expose the underlying material 37 which, in this case, must be
hydrophobic. Removal of facing only from the field printers may be
accomplished by abrasive or chemical etching against a prepared
platen, much as before described. Initial preparation is thus
simplified, it being safe to merely roll up the duplicate with a
thin wet fluid and then roll it up with a lipid fluid.
DUPLICATE RELIEF PLATE, TYPE III (FIG. 14). This duplicate is of
hydrophobic material 39 which can be topically rendered hydrophilic
by physical or chemical treatment. Among suitable materials are:
cellulose esters such as cellulose acetate, cellulose acetate
proprionate and cellulose acetate butyrate; rubber, polyvinyl
chloride; reversibly-insolublized forms of gelatine, casein or
shellac; and metals, especially amphoteric metals. Treated layer 38
is intended to represent an oxide-free surface on rubber, polyvinyl
chloride and like materials; a surface-hydrolyzed region of
cellulose esters and other topically hydrolyzable organic
materials; a topically re-solublized region of materials such as
the suggested proteinous organics gelatine, casein and shellac; a
hydrophilic silicate film upon metals; and a roughened, grained, or
oxide-free region of metals and materials in general. It will be
noted that the whole surface, including the plate recesses, is
given a hydrophilic treatment. Chemical treatment may employ
flooding with a treating solution or exposure otherwise to a
suitable reagent. Physical treatment means may include abrasive
blasting or exposure to a reducing flame.
Pre-press preparation may be essentially as was described for a
duplicate, Type I.
DUPLICATE RELIEF PLATE, TYPE IV (FIG. 15). This duplicate may be of
hydrophobic convertible material 39 similar to that of a duplicate,
Type III. A characteristic difference of this type of duplicate is
that the hydrophilic layer 39 is only local to the field printers
20. To only treat field printers, the duplicate may be lightly
impressed upon a platen or the like which has been sparsely wetted
with treating solution, or is abrasive, essentilaly as before
described for other duplicates. Also among metals which may be used
for this duplicate are those which can be amalgamated, e.g.,
copper. An electroformed copper duplicate may, for example, be
lightly rubbed against a superficially mercurialized nickel platen,
and mercury will be taken up by the slightly relieved field
printers. The mercurialized field printers will be receptive to a
wet ink and repellant to a lipid ink.
Generally, pre-press preparation may be as before described,
whereby the treated field printers are first given a wet fluid
before the composite image 12',13' is rolled up with a lipid fluid.
However, a freshly mercurialized duplicate might safely have the
lipid fluid applied first.
DUPLICATE RELIEF PLATE, TYPE V (FIG. 16). This duplicate may be of
hyprophobic convertible material similar to that usable for a
duplicate, type III, but which is amenable to topical hydrophilic
treatment by chemical means rather than physical means. The
slightly relieved field printers 20 are first carefully coated with
a resist 41 which will be protective against treating solutions.
Resist 41 may be applied to the field printers by lightly
impressing the duplicate upon a platen or other flat surface which
has been thinly coated with the resist. Several repeated slightly
displaced impressions may be made to assure that the field printers
have been adequately coated. Te duplicate may then be immersed in
or flooded with an appropriate treating solution which will render
unprotected portions hydrophilic. As may be seen in FIG. 16a the
treated layer or region 38 also includes the recesses. If resist 41
is not also suitable as a base for the lipid ink, or cannot be
rendered so, it is removed with appropriate solvent or reagent.
By alternative means shown in FIG. 16b the duplicate can be given a
hydrophilic layer 38 only upon the composite image 12',13' . As
before, the field printers 20 are first coated with a resist 41.
Then treating solution is applied with a slightly elastic roller,
or the duplicate is inverted and carefully and lightly impressed
into a thin film of treating solution. The embodiment of FIG. 16b
is preferred for use with very thin wet inks, as the hydrophobic
recesses will tend to prevent accumulation of wet ink therein.
Pre-press preparation for either embodiment will require that the
composite image rather than the field printers receive the wet
fluid while the field printers receive a lipid fluid. The
hydrophobic field printers enable the composite image to be wetted
or inked first, e.g., by roller application of the "dark" wet
ink.
In describing pre-press preparation and topical hydrophilic
treatments as they may specifically relate to duplicate reliefs, it
is understood that generally similar procedures may be used to
prepare original plates prior to their placement on a press if the
original plates do not embody materials already selectively
receptive to respective inks, or which have not had ink-base
applied during some phase of platemaking.
On the press, the respective inks are applied across the whole of
the plate surface, e.g., by the use of rollers, but only take to
their respective plate elements (or to ink-base thereon). Either
the wet ink or the lipid ink may be applied first, between
impressions, whichever sequence is found most satisfactory for a
particular plate and for the press. It may be found practical for
certain applications to emulsify the two inks into a single
composite ink which is singly applied, the emulsified components
taking only to their respective plate elements. An emulsion may,
for example, have a form somewhat as described by Mehl, U.S. Pat.
No. 1,958,311, but wherein his oridinarily colorless phase
containing sodium hyposulfite (sodium thiosulfate or "hypo"is
appropriately colored or of "dark" tone. A suitable emulsion might
also be obtained merely by physical agitation. Except that the inks
are generally applied across the whole plate surface, I do not
limit practice of this invention to specific modes of inking.
PLANOGRAPHIC PLATES
The relief plates hereinbefore described provide a basis for the
ready understanding of planographic equivalents. A planographic
plate made according to this invention comprises three topical
phases: a "dark phase" which (when inked) prints the composite
image in a "dark" ink; a "color phase" which (when inked) prints
the color fields; and a "3rd phase" which (usually) is un-inked and
non-printing although it may be wetted. One of these topical phases
may be the surface of the plate body, the other topical phases may
be in slight relief thereon. In common with other planographic
plates such slight relief is insufficient to keep any of the plate
phases from contacting the paper in the case of direct printing, or
from contacting the transfer blanket in the case of offset
printing.
Although there are three topical phases not all of my planographic
plates require a system of three immiscible fluids, as might seem
necessary. Those plates which do use three fluids are referred to
as "lithographic" plates to distinguish them from other
planographic plates.
As regards my lithographic plates: for use on the "dark phase" I
may employ a "dark" tone lipid ink of letterpress consistency or of
the usual lithographic consistency; for use on the "color phase" I
may employ a polyvinyl alcohol ink of a viscosity roughly midway
between water and that of the lipid ink, but preferably closer to
that of the lipid ink with which some slight and slow mingling is
tolerable; for use on the "3rd phase" I may employ water or an
aqueous wetting solution (which will be colorless when the 3rd
phase is not intended to print). The preceding phase assignments
are preferred.
Assuming the "3rd phase" to be non-printing, I may interchange the
assignment of my three fluids--whichever is used upon the "3 rd
phase" will be colorless; whichever is used upon the "color phase"
will be of a selected color; and whichever is used upon the "dark
phase" will be of "dark" tone. When the "3rd phase" is to print,
whatever fluid is used thereon will be of an appropriate tint or
color as later explained. The "3rd phase" will usually have the
largest area whether printing or non-printing, and for economic
reasons water or an aqueous fluid is best used thereon. Instead of
using polyvinyl alcohol as one of the three fluids any other
functional equivalent may be substituted which is suitably
immiscible with water and with lipids, and instead of the
particular combination of fluids mentioned other mutually
immiscible fluids may be used. My plates will, however, be
described as they may use the preferred phase assignments and
lipid, wet, and polyvinyl fluids.
The three immiscible fluids do not have to exhibit selective
affinity for the respective plate phase with which they are
associated, although such properties are desirable for one or more
of the fluids. The selective receptivity of the three fluids on the
plate is more directly a result of the mutually repellant
properties of the fluids themselves, not of "repellancy" properties
of plate materials. As will be appreciated from the procedural
descriptions, the first fluid applied during plate preparation will
reject the next fluid to be applied, while both the former fluids
will repel the third fluid. My lithographic plates may be as
follows or be variations thereon:
LITHOGRAPHIC PLATE, "COMMON" TYPE (FIG. 17d). This plate is
prepared similarly to a common lithographic plate, inasmuch as the
plate image is in slight (planographic) relief and formed of
resist. Referring to FIG. 17a-d:
a. A positive halftone composite plate image 12',13' is photoformed
in slight relief t upon a body 43 which may be a lithographic
metal, e.g., aluminum or zinc. As conventional the plate surface 43
is hydrophilic, e.g., by virtue of silicate treatment or graining,
and the photoformed resist image 12',13' is hydrophobic and
lipidophilic. Use of a diazo-sensitized, silicate treated aluminum
plate described by Jewett in U.S. Pat. No. 2,714,066, previously
cited, is preferred and here assumed. As recommended by Jewett, and
in keeping with general good practice, the image after exposure may
be rubbed or rolled up with a lithographic "development" ink.
However, for convenience in making a second exposure herefor
necessary, the development ink may be of a kind which drys or is
non-sticky but which may later be re-rendered tacky, e.g., by
partial solvating, to assist in ink-up.
b. The plate is now re-coated with a photosensitized hydrophil 44.
It is permissible for photocoat 44 to be applied in slight excess
above the image 12' ,13', or flush as is shown and preferred.
c. Portions of photocoat 44 coincident with long components of the
composite image and contiguous to halftone dots 12' respective
thereto, are exposed to actinic light through a light-stencil 18 or
equivalent, essentially as before described. To assist in
receptivity of polyvinyl alcohol ink which will be used upon
light-reacted portions of photocoat 44, the exposure is partial.
(As mentioned, the polyvinyl alcohol ink or fluid has a viscosity
giving it properties roughly midway between a wet fluid and a lipid
fluid.) The partial exposure is sufficient to render exposed
portions poorly water-wettable without being completely
hydrophobic, and substantially insoluble in a polyvinyl ink or
alcohol. It will now be understood that many common hydrophilic
light-insolublized photoresists may be used for photocoat 44, e.g.,
of gum arabic, gelatine, shellac (hydrolyzed), casein (hydrolyzed),
or mixtures of these with each other or other materials and
compounds. Also useful for photocoat 44 are the visible-light
sensitive materials described by Oster in U.S. Pat. No. 3,097,096,
previously cited, particularly as mentioned in column 7, line 53,
which remain hydrophilic after a full exposure. These can be
specially tailored for present purposes, i.e., made less complete
hydrophils, by including an amount of monomer which forms a
hydrophobic polymer in replacement of an equal amount of the usual
monomer.
d. The plate is developed by a suitable solvent to remove unexposed
portions of the photocoat 44. Prior to this development, the plate
should be rolled up with the polyvinyl alcohol ink or an
equivalent. This may be done while the development ink on the
composite image is tacky. After development, a light counter etch
may be given to rid areas 43' of any residue.
Remaining portions 44' of the photocoat now act as the field
printers 20 or the "color phase"; the composite image 12',13'
comprises the "dark phase" ; and areas 43' are the "3rd phase" and
will be wetted with water or other aqueous fluid ordinarly
colorless.
LITHOGRAPHIC PLATE, "DEEP-ETCH" TYPE (FIG. 18d). This plate is
prepared similarly to a so-called "deep-etch" lithographic plate,
inasmuch as the image is in slight intaglio. Referring to FIG.
18a-d:
a. A positive composite halftone image 12' ,13' is obtained in
slight intaglio (about 1 mil) by wellknown means, on a plate 52
which has a grained surface 51' or on a silicate-treated plate. In
the latter case it will be desirable to "deep etch" the plate
through the stencil image by means of light abrasive blasting
rather than chemical means. As conventional the image is of lipid
ink-base.
b-c. (Not shown) the plate is re-coated and exposed essentially as
in (b) and (c) for a negative plate.
d. The plate is developed as in (d) for a negative plate. The final
plate has only the field printers 20 or "color phase" in slight
relief.
In preparing a "common" lithographic plate, instead of re-coating
the plate with a second sensitized material 44, unexposed portions
of the original photocoat (if it be of hydrophilic material) may be
allowed to remain for use as of the second material. The plate may
be rinsed after the initial exposure and application of development
ink, just sufficiently to float off development ink from the
portions other than the image dots. If necessary after such
rinsing, the remaining unexposed material may be re-sensitized by a
brief bath in a sensitizing solution. For this alternative
procedure the original photocoat may be somewhat thicker than is
usual.
For use with three immiscible fluids bi-metallic and tri-metallic
lithographic plates can be made, the former including one phase of
non-metallic material, e.g., an organic resist. A bi-metallic plate
may, for example, be obtained merely by electrodepositing upon a
grained aluminum base, a lipidophilic metal such as copper in place
of the ink-base image of a "deep-etch" plate. By a slight
variation, the metal image may be slightly raised. A tri-metallic
plate may comprise a base metal and two other metals selectively
applied through stencils. The base metal may suitably be grained to
be hydrophilic, and may act as the "3rd phase." Assuming selective
application, copper may be electrodeposited through a negative
stencil of resist to form a grease-receptive composite image or
"dark phase", and for the "color phase" zinc may be analogously
applied. The base metal may also be zinc, which has been grained.
For each deposited metal an appropriate ink-base or development ink
should be applied before removal of the stencil. Various other
combinations of metals may be used. By employing various known
means of selective removal, bi-metallic and tri-metallic plates may
initially be in the form of flat sheets of laminar structure.
By means now disclosed I may obtain a planographic plate that does
not require the use of three mutually immiscible fluids:
MAGNETIC PLATE (FIG. 19d). This plate 45 embodies a composite
halftone image 12' ,13' formed of magnetized hydrophobic material,
and field printers 20 formed of non-magnetized hydrophobic
material. The plate body 45 is non-magnetic and has a hydrophilic
surface 45'. The usual operation of this plate will be understood
after a further description of its construction, major procedures
for which are shown in FIG. 19a-d. FIG. 19e-f shows steps in
pre-press inking. Referring to FIG. 19 in its respective parts:
a. A positive halftone composite image 12' ,13' is photoformed of
magnetizable hydrophobic material upon a support 45, e.g., of a
lithographic metal 45 which has been grained or otherwise rendered
topically hydrophilic. It is here assumed that support 45 is
aluminum with a sodium-silicate layer 45'. The magnetizable
material and means of forming a plate image thereof may be as
described by Hamm in U.S. Pat. Nos. 2,819,963; 2,823,999 and
2,856,284. The magnetizable material may initially be hydrophilic,
but must become hydrophobic after exposure to actinic light.
Although the magnetized image 12',13' is shown in slight relief t,
it may instead be embedded in the plate body in the manner of
ink-base used in a "deep-etch" plate. In such case the magnetizable
material need not be photosensitized, being formed through a
stencil as is ink-base. Preferably, as described by Hamm and here
assumed, the actual magnetization takes place subsequent to the
photo-formation of the image in the plate, but may less suitably be
done while the image material is still a uniform layer.
b. The plate is re-coated with a photosensitive material 46 which
is hydrophobic in its final form, if not before. Material 46 is
here assumed to be of a "negative" light-insolublized type.
c. Photocoat 46 is exposed to actinic light where coincident with
long components of the composite and contiguous to halftone dots
12' respective thereto. A light-stencil 18 or equivalent may be
used, essentially as before described for other plates.
d. Photocoat 46 is developed so that only exposed portions 46'
remain. These form the field printers 20. Bare areas of layer 45'
are (usually) non-printing and thus will receive a colorless fluid,
e.g., water. However, the water will contain suspended or floated
particles of black iron or a black ferrous oxide. These particles
separate out from the aqueous carrier and enable the water on bare
areas of layer 45' to be clear. The particles are magnetically
attracted only to the magnetized composite image 12',13'. The
composite image 12',13' also receives a lipid ink as do the field
printers 20, the same lipid ink being applied to both and being of
a selected color. Inking may be as follows:
e. After the plate has been given an overall wetting, e.g., by
sponging with clear water, it is rolled up with a lipid ink of the
same color that will be used in the press run to print the color
fields. As may be seen, this ink covers the field prints 20 as well
as the composite image 12',13'.
f. The plate is next flooded lightly with a clear aqueous fluid
carrying finely divided back magnetically-susceptible particles 48,
e.g., black ferrous oxide Fe.sub.3 0.sub.4. The particles 45 (which
may themselves be magnetic although this is best avoided) are
attracted to the magnetized plate image 12',13' even though the
plate image has a coating of lipid color ink. The clear fluid
carrier re-wets bare areas of layer 45' which are non-printing. It
can be helpful if the particles 48 are of blue-black or
greenish-black tone rather than neutral black or of arbitrary dark
tone. Toning may be accomplished by chemical agents, individual
coating of the particles, and by other means which may be obvious
to metallurgists. When an impression is made from this plate, the
colored lipid ink on the composite image 12',13' acts as a binder
for the particles 48. However, the requisite "dark" tone for the
printed image is obtained because the deep tone of the particles 48
dominates the chromaticity of the colored lipid ink. The
utilization of ink as a binder is in particular distinction to
means of binding or fixing as employed by Hamm.
Instead of an aqueous vehicle for particles 48, and for wetting
non-printing areas, I may use an organic solvent immiscible with
water, e.g., carbon tetrachloride; for the field printer and
composite image I may then use materials which will not be
dissolved thereby and which remain receptive to wet ink, e.g.,
hydrophilic materials which are or have been treated as described
to remain hydrophilic. My color ink will accordingly be wet so as
not to bleed with the organic solvent, and also of film forming,
e.g., mucilaginous nature to bind particles 48. The plate will need
no special surface treatment in order to be "wetted" by carbon
tetrachloride or like fluid.
I may form all printing elements in substantially high relief to
function as a "magnetic" relief plate. In such case the only fluid
which the press need apply is the color ink; particles 48 can be
dusted on or equivalently applied.
For either my planographic or relief "magnetic" plate, instead of
dusting, particles 48 may be caused to transfer to the plate from a
magnetized roller weaker in strength than the plate image, or from
a bed or reservoir, said roller or bed being closely proximitous
but not in actual contact with the plate. When particles 48 are to
be carried by a fluid, they may equivalently be floated upon a film
of such fluid or may be carried by a foam, and the plate may make
grazing contact with said film or foam.
XEROGRAPHIC PLATE (FIG. 20b). In common with other xerographic
"plates" or surfaces, and with known xerographic techniques for
forming two (or more) differently-colored unfixed ink images upon a
single photoconductive surface prior to their simultaneous transfer
to paper or other fuel receiving surface, I may proceed as follows
with reference to FIG. 20a-b:
a. By known xerographic means, using a "dark" unfixed electrostatic
xerographic ink 51, a positive halftone composite image 12',13' is
deposited upon a photoconductive surface 49.
b. By known xerographic techniques of re-imaging and double-inking,
field printers 20 are formed of an unfixed electrostatic
xerographic ink 52 of selected color, deposited on the
photoconductive surface 49. The field printers 20 are in register
with predetermined components of the composite, e.g., with the long
components as is generally preferred, and are contiguous to
halftone dots respective to said components, e.g., halftones dots
12'. To deposit the color ink field printers in register with the
desired image components, the photoconductive surface is
selectively discharged by exposure through a negative or reverse
light-stencil as has been previously described. This stencil is in
lieu of the usual picture image which would be used for forming a
second ink dposit on the plate or surface. The color ink will not
take to or overprint the "dark" ink previously deposited; such
non-occlusion is inherent in the known technique of forming a
double-inked xerographic surface. It is understood that the
photoconductive surface 49 is upon an electrically conductive
support 50, which is grounded.
The unfixed inks on the xerographic "plate" or surface are now
ready to be electrostatically transferred to a receiving surface
whether paper or other material of an electrically insulating
nature, said transfer being simultaneous and analogous to a single
impression. For purposes of the appended claims, the respective
deposits of dark ink and colored ink on a xerographic surface, are
considered equivalent to photomechanically formed relief and
planographic elements that otherwise would receive dark and color
inks for transfer to paper and the like.
ELECTROSTATIC PLATE (FIG. 21). This plate comprises an electrically
conductive support 52 upon which is first formed, in slight relief
t, a positive halftone composite image 12',13' (FIG. 21a).
Subsequently, field printers 20 are formed coincident with long
components of the image and contiguous to halftone dots 12'
respective to said components (FIG. 21b). Various means of
photoforming these elements will be obvious from prior description
and from known platemaking art, except that particular materials
are employed.
The composite image and the field printers are of different
respective materials, each being electrically non-conductive and
triboelectric. They are selected to have the mutual property that,
when rubbed by a particular other material one plate material will
assume a negative elestrostatic charge and the other plate material
will assume a positive electrostatic charge. Alternatively, two
different rubbing materials may be used, as will be explained.
Virtually all non-conductors will exhibit the property of assuming
a static charge when rubbed, this being known as the triboelectric
effect. The electrical sign of the charge on a rubbed material will
depend on the two materials which are being rubbed, that is, on the
particular plate material and the particular rubbing material(s)
acting upon it. To my knowledge the triboelectric properties of
materials have not been summarized in physical texts, patent
literature or elsewhere, but simple experiment can determine which
material combinations may be best suited for commercial
applications of this plate. Some materials will be suggested.
The single rubbing material may take the form of a brush or roller
bearing lightly against a cylinder upon which my plate may be
mounted. The brush or roller may comprise, for example, hair or
flannel or like organic material. One plate material may be hard
rubber, a resin or polymer of rubbery consistency, or another dry
organic substance or composition; the other plate material may be
glass, finely-divided glass particles suspended in a
sodium-silicate or potassium-silicate matrix, or another cermaic or
inorganic dry and non-conductive substance or composition. The
rubbery or resinous organic material will assume a negative static
charge when rubbed, and the glassy or ceramic material will assume
a positive static charge when rubbed. The positive charge will be
weaker than the negative charge, but while equality in strength of
the respective charges is desirable, it is unnecessary. Instead of
rubbing with hair or flannel or the like, I may rub the plate
elements with silk or the like. This will result in the glassy or
ceramic plate material assuming a positive charge which is stronger
than the negative charge on the rubbery plate material. To secure a
more equal balance of respective charge intensities, I may rub the
plate with a blend of flannel and silk, or a blend of other
materials, or a single material specially selected to have
equivalent rubbing properties as a blend. Where two different
rubbing materials are used I may form each into a separate brush or
roller; then I may, with two rollers or one roller and one brush,
equalize the respective charges on the plate materials by
differentially regulating the rubbing speeds of the two rollers or
of the one roller relative to the fixed brush. With rollers,
rubbing may suitably be counter-rotary to the direction of the
plate cylinder.
The functional assignment of the two triboelectric plate materials
is arbitrary. I may, for example, employ the rubbery or resinous
material for the composite image 12',13', and the glassy or ceramic
material for the field printers 20. The composite image will thus
become negatively charged, and the "dark" electrostatic ink applied
must be positively charged, relative thereto, so it will only be
attracted to the plate image. The field printers will become
positively charged, and therefore the color electrostatic ink must
be negatively charged, relative thereto. Means to charge and apply
electrostatic inks are well-known. After both inks have been
applied to the plate they may be simultaneously transferred to
paper or another receiving surface. These electrostatic inks may
most suitably be in the nature of xerographic inks, being comprised
of fine solid particles which are binded or fixed by heat after
electrostatic transfer to a dry non-conductive receiving surface
such as paper. Less suitably, the electrostatic inks may,
respectively, be fine droplets of a fluid ink which droplets have
been given an electrostatic charge, as in electrostatic paint
spraying. The latter practice will require plate-charging means
other than rubbing, as will be described later.
It is not necessary that triboelectric materials be chosen which
assume respective charges opposite in sign. Charges of the same
sign but of differing intensity are, as is well-known, equivalent
in an electrical sense to an absolute difference in sign. In such
case, the charges given to the respective inks may both be of a
common sign opposite to the sign common to the charges on the
respective plate materials, but of proportionately different
intensities.
Instead of rubbing, I may charge my different plate elements from a
single corona spray apparatus, analogously as in xeroprinting. In
such case, the different plate materials will both assume the same
sign, but of different intensity. In a claim where I may refer to a
difference in charges, it is not necessarily meant to imply a
difference in sign.
Instead of employing two plate materials which are caused to assume
differential charges, I may for one or both substitute an
"electret," as defined in the International Encyclopedia of
Chemical Science, published in 1964 by the D. Van Nostrand Company,
Inc., Princeton, N.J. When the composite image is of an electret
material and the color fields are of an electret material, the
image can be given a permanent electrostatic charge of one sign,
and the field printers can be given an electrostatic and permanent
charge of opposite sign. The same electret material may be used for
both plate elements. The different permanent charges are caused by
allowing each of the two plate elements to crystallize or set while
in the presence of a strong electrostatic field of respective sign.
When both plate elements have a permanent charge the need for
rubbing or induction otherwise is completely eliminated. If only
one plate element is formed of an electret material, it may by
similar means be given a permanent charge opposite in sign from
that which the other plate material will assume when rubbed or
externally charged.
In all the given examples of plate construction it has been assumed
that the field printers are associated with the long components of
the composite image, as such association is generally preferred.
Field printers may as readily be formed in association with short
components of the image contiguous to halftone dots 13', by
employing a light-stencil or equivalent in which (for an ordinary
or positive stencil) areas 18a and 18b are positionally reversed.
For a plate so-formed, the field printers must be given an ink of
selected "cool" rather than "warm" color. It will be generally
understood that because the color field pattern bears no pictorial
information, the same light-stencil or compositing screen may be
used for widely differing subject matter. Thus, with suitable
industry or shop standards only the copy and composite image need
vary for each different printed picture. Also, if a particular
color is decided upon for the color fields, e.g., a red, as
generally recommended, a printer need not change inks for the
printing of different pictures. On the same press a printer might
run conventional work in either the "dark" or the particular color
field ink.
Although I have described use of a light-stncil or equivalent
thereof by itself, a stencil or equivalent may be superimposed with
a photographic composite image and an exposure may then be made
through such joint assembly. By such means any photocoat which may
be atop previously formed composite image plate elements 12',13'
will not be exposed. It will also be possible by such procedure to
form the field printers first, and then to form associated
composite image dots in voids left in the field printing elements,
in addition to the composite image dots which fall between the
field printing elements.
I do not intend to restrict any lithographic and magnetic plates to
use of a metal body or base material, as was described. Many
non-metallic substitutes for lithographic metals are known;
commonly used for such purposes is a surface-hydrolyzed cellulose
ester, e.g., cellulose acetate.
Wherever I have given actual dimensions or figures, these are
provided with the sole intention of indicating a general order of
magnitude and should not be construed as being limiting.
While all my plates are shown as being flat, they may be curved at
any suitable stage in their preparation for use on rotary
equipment, with due consideration as to their particular materials.
With reference to my lithographic plates and my magnetic plate,
wherever nonprinting areas are mentioned they may be caused to
print by using a non-colorless fluid thereon. Such a fluid may be
tinted or of fuller hue selected as hereinafter described in the
section "Gamut Enhancement," such practice being useful in lieu of
the optional use of tinted or colored paper or other receiving
surfaces. As described for my relief plates, fluids used on my
lithographic plates can be emulsified, e.g., the lipid fluid and
the aqueous fluid where these are two of three. The press need only
have two fountain and distribution systems in such case, one for
the emulsion and one for the third fluid which will be separately
applied. I do not exclude use of a three-phase emulsion and but one
active fountain and distribution system on the press. A suitably
formulated semi-polar polyvinyl alcohol ink might act as an
emulsifier or intermediate between an aqueous wetting fluid and a
lipid ink.
My relief plates may be run on a lithographic press, whether direct
or offset, which has been modified to accommodate the slightly
greater thickness ordinary to relief plates by virtue of the
relief, and which uses a rubber or like roller for the wet ink
instead of the more common molleton or cloth-covered roller usually
used for the aqueous fluid. Ordinarily, my relief plates are usable
on letterpress equipment that has additionally been provided with a
fountain and distribution system for the wet ink. Here also, the
roller for the wet ink is best not cloth covered, as the nap will
tend to apply the wet ink to the image recesses. For use on
flat-bed or platen presses my relief plates may be made "type high"
by attachment to a suitably thick backing. Generally, my relief,
lithographic and magnetic plates are best used for indirect or
offset printing employing an intermediate transfer surface such as
a rubber blanket.
My lithographic plates may be used on lithographic equipment,
whether direct or offset, which has been provided with a third
active fountain and distribution system for the third fluid, except
if two or all three of the fluids have been emulsified. A molleton
or cloth covered roller, if used, is best limited to the fluid
having the least viscosity.
It will be possible to lock up a relief plate of my construction in
a form along with conventional relief printing elements such as
type, line cuts and ordinary halftones. Such supplemental graphics
may, if conventionally made, receive the same lipid ink used in
printing the multicolor picture. However, all or some of these
supplemental graphics may be formed in whole or part of hydrophilic
material or material of hydrophilic surface (by means derived from
general disclosures herein), which parts once wetted, will
thereafter receive the wet ink. When ordinary type is among the
supplemental graphics, it will usually be necessary that the lipid
ink be the "dark" ink, except if it is permissible for the type to
print in color. By such provisions, the multi-color picture may be
printed simultaneously with other graphics whether pictorial or
otherwise and which may be in monotone or "single-impression
duotone," e.g., respectively either in black or in red, or in black
and red. Obviously, a jobber may without modification of the press
or inking system thereof, run ordinary monotone or
"single-impression duotone" work alone.
As is known, a duotone may be a line cut, a combination of line and
halftone elements, or be wholly in halftone, and my
"single-impression duotone" may comprise similar elements. A
"single-impression duotone," comprising two whole halftone images
(whether one or both are color separations) in general
superposition upon a single plate, and wherein one is hydrophilic
and the other is hydrophobic each receiving a respective colored or
toned ink, is considered to be an obvious derivative of this
invention. Two conventional halftone photographs would be used to
form the respective plate elements, instead of using one halftone
(composite) photograph and a lightstencil or equivalent. With a
"single-impression duotone" a variety of color effects may be
achieved, some of which may be somewhat natural-appearing, e.g., as
when complementary colors are used, and even with red and black or
other dark ink. Such a plate may be substituted for plates
hereinbefore described, and many of the general advantages of my
invention may be had.
A "single-impression duotone" comprised of two whole halftone
images may be as shown in FIG. 25. The halftone images may be color
separations in positive form. Use of a green separation and a red
separation is here assumed. Preferably first, halftone elements 55
corresponding to the positive green separation (in its entirety)
are formed in relief in a body material 57. Subsequently, halftone
elements 56 corresponding to the positive red separation (in its
entirety) are formed in relief of "fill" material which has been
applied to the recesses of the first plate image 55. This formation
is analogous to the formation of field printers for my other relief
plates. Assuming that body material 57 is of metal, e.g., copper,
and will be hydrophobic and receptive to a lipid ink, the plate
image 56 is photoformed of hydrophilic material, e.g., of a
partially-exposed photosensitized hydrophilic organic such as
gelatine, which will be receptive to wet ink. Many other
combinations of materials, and the use of various surface
treatments, will be obvious from preceding parts of this
specification. Instead of a relief plate as shown here,
lithographic, magnetic, xerographic and electrostatic equivalents
may be made.
The particular color separations here given by way of example, are
as described by Land in U.S. Pat. No. 3,034,890. Also in accord
with Land's teachings therein, halftone elements 55 for the
positive green separation are inked with a red ink, and halftone
elements 56 for the positive red separation are inked with an ink
of dark tone. (I do not limit myself to the neutral tone Land
prescribes, or to a substantially pure red.) Because of the
particular assignment of hydrophobic and hydrophilic plate
materials given by way of example, the red ink will be lipid and
the dark tone ink will be wet.
By means of the aforementioned plate I am able in one impression to
obtain an apparent multicolor print which by other means would
require two impression, two plates, and unorthodox and judicious
press register. It will be appreciated that by first forming the
image which is to receive color ink, I am able to minimize the need
for reduced density in the image that receives the dark ink (as
recommended by Land). This is because the first-formed image, on a
random basis precludes or prevents the complete facial formation of
many individual halftone elements of the second image. Though I
have shown my "single-impression duotone" as it may be utilized to
print an apparent multicolor picture such as Land describes in U.S.
Pat. No. 3,034,890, I do not limit my duotone plate to use of
particular color separations or to particular colored or toned
inks.
For rotary letterpress, and lithographic and other planographic
plates, where a single large plate is used instead of various
graphic elements locked in a form, such plates in addition to a
natural multicolor picture may also print equivalent supplemental
graphics, whether in monotone or duotone, using the inks necessary
for the multicolor picture. The various options herebefore
described are considered an indirect advantage of my intention when
commercially practiced.
For convenience, only major and exemplary platemaking sequences
have been given. It will be realized that even for conventional
plates procedures will vary in different shops and as described by
different texts. Variations in my procedures yielding an equivalent
functional result or product, and substitutions of materials
whether equivalent or superior if determinable merely by experiment
or by ordinary expert knowledge, are considered to be within the
present scope.
GAMUT ENHANCEMENT
Non-Maxwellian prints and projections or other optical displays
(especially prints) have heretofore suffered from chromatic
inadequacies, generally a weakness of color from one or another
primary region of the spectrum, and a corresponding weakness or
absence of certain secondary colors somehow dependent thereupon.
Thus, while the range of apparent colors has in all cases been more
than would classically be expected, the overall effect was less
than could be obtained by conventional "full color" reproduction
processes. It has not been obvious how such inadequacies can be
avoided or further minimized, or that improvement is theoretically
possible without progressing from two to three stimuli.
The general practice of this invention need not employ the means of
gamut enhancement here disclosed, as the selection of separations
and stimuli as taught by Land will yield satisfactory results for
most purposes. As does Land, I would usually use a red long
separation and a green short separation although the use of other
color separations is permissible. Thus, as Land describes and is
also satisfactory for this invention, an Eastman Kodak Wratten
filter No. 24 or No. 25 may be used to obtain a long separation on
a panchromatic emulsion, and a No. 57 or No. 58 (whose transmission
Land presumably shows in Scientific American) may be used to obtain
a short separation on a panchromatic emulsion, and generally
related filters may be used instead. I am aware of no Eastman Kodak
Wratten filter No. 69 as Land mentions in U.S. Pat. No. 3,034,890
column 2, line 59. I do not limit myself to any particular values
of gamma, as such values and other processing procedures for
photographs are best determined in practice by simple and obvious
means. For regulating the relative intensity of the long and short
components of the composite image, and as a means of color balance
which avoids need for inequality of size between the color fields
and spaces of the receiving surface therebetween, I may process the
respective separations to different densities or obtain different
densities at the time of exposure. Generally I would make both
separations slightly more dense than is usual, particularly in
positive highlights, and make the short separation slightly denser
than the long separation, but I do not limit myself to such
practices. Color balance can also be affected by use of appropriate
color compensating filters during photography of the separations,
and, in the final reproduction, by use of differential gloss or
texture between the color ink and/or the "dark" ink relative to the
receiving surface.
The use of a white stimulus is of particular advantage inasmuch as
white paper can be employed. Color fields of a "warm" color, e.g.,
a red, printed on white will prove somewhat more effective than
color fields of a "cool" color, e.g., a green. As Land mentions, a
white paired with a warm stimulus may with advantage be of a cool
tint. I recommend that a white paired with a cool stimulus be of a
warm tint. The particular warm and cool tints may be as later
described. Land defines his use of the terms "warm" and "cool" by
reference to Webster's New International Dictionary, 2nd Edition
Unabridged, which definitions are also acceptable for purposes of
this specification.
If in conjunction with other of my enhancement means the white is
cool-tinted, the tint is preferably greenish rather than the bluish
tint recommended by Land. Similarly, a white which is warm-tinted
is preferably reddish rather than yellowish. When such specific
tinting is done conjunctive with other of my enhancement means to
be described, the tint may be very pale yet yield satisfactory
results. However, I do not exclude use of receiving surfaces of
deeper tint or fuller hue correspondent to my preferred tints. When
my complete enhancement means are not to be employed, tinting or
fuller coloring, if used, may more freely be of any warm or cool
hue appropriate to the printed color fields.
In non-Maxwellian prints made according to the existing art, and
which use the two stimuli red and green, red and cyan, red and
white, green or cyan and white, red and a cool tint, or green or
cyan and a warm tint, which pairs are generally more effective than
other possible pairs, the color deficiency in the apparent gamut
will occur in the blues. There will be a noticeable weakness or
absence of true blues, blue objects appearing at best a deep
turquoise or deep cyan. This is not wholly unsatisfactory for in
nature and man-made objects large expanses of true blues are rare,
and deep turquoise and like tones have come to be popularly
accepted as blues. However, a degree of naturalness is lost,
because blue is present in varying amount in most common colors and
objects. Secondary colors classically dependent on blues will be
either absent or degraded, e.g., purples, which if present at all
will seem wine-colored or reddish. My gamut enhancement means are
therefore primarily directed toward the enhancement of blues.
Because my enhancement means are simple and might appear to be
obvious, I will review other attempts at the same.
It might seem that by using a full blue-green (cyan) separation in
conjunction with a red separation, a fuller rendition of blues
would take place in the final print. The short separation filters
Land suggests do not transmit broadly in the blue region of the
spectrum. However, the use of a full blue-green taking filter does
not prove satisfactory in practice; this is probably because no
more than two packets of color information, "long" and "short," are
presented to the eye in the final print regardless of the bandwidth
of the stimuli or the broadness of the separations, as Land has
theorized. In the same sense, classical 2-color or complementary
systems such as red and cyan or blue and yellow fail to reproduce
the full gamut, although in theory all colors should be
encompassed. Thus, Land acknowledges that his green taking filter
does not transmit blues too satisfactorily (U.S. Pat. No. 3,147,699
column 7, line 30), but with good reason he does not propose to
increase its transmission of blues.
To enhance perception of blues, Land proposes the use of a
cool-tinted illuminant or stimulus of pale blue, rather than an
achromatic white or a warm tungsten or yellowish white (3,003,391
column 7, lines 19-23). Such means does enhance blues, but by
default, as it desaturates other colors at the same time.
Equivalent would be the use of a blue-tinted screen for projected
non-Maxwellian pictures.
Specifically as regards a print rather than a projected picture,
Land recommends that the viewing light and/or paper be of cold
bluish tone in order to yield satisfactory blues (and greens), and
that the densities of the neutral tone image be soft grays and of
reduced contrast rather than deep blacks (U.S. Pat. No. 3,034,890
column 3, lines 54-62). As mentioned I prefer a greenish tint, and
am not solely dependent upon the short stimulus for blue
enhancement as will be seen.
In further attempt to enhance blues Land proposes use of a third
stimulus of blue and a blue separation (U.S. Pat. No. 3,003,391
column 6, line 24-36). Such means, while fully operative and
satisfactory for projected pictures because there is no halftone
structure or inherent limitation to the relative intensities of the
illuminants or stimuli, is undersirable for the printed page. The
use of only two stimuli on a printed page, particularly when one is
white or of a pale hue, results in greater overall brightness and
improved color resolution. The latter is due to the greater number
of color field repeats within a given area for color fields of a
given size.
It might seem that for subject matter rich in blues a blue short
separation could be used instead of a green separation or a
blue-green separation. This does not prove satisfactory for reasons
of uncertain nature; probably because the red-green visual
mechanism is dominant.
Of course, Dr. Land's "short wave reversal" combination of stimuli
might be used, e.g., employing both blue paper and printed blue
color fields. However, for printed reproductions the brightness and
contrast would be low, except possibly with the fluorescent
pigments or dyes he proposes; in the latter case the viewing
illuminant must be rich in ultraviolet.
My gamut enhancement means may best be understood by assuming, for
the moment, that the long separation records no blues or greens,
that the short separation records no blues or reds, and that the
composite image printed on the paper is in black ink, e.g., in a
neutral or achromatic tone as specified by Land. The original copy
is assumed to contain all colors, black and white. Black ink dots
of the long component (dots 12') will thus represent the quantity
of "minus red" or cyan in the copy, or the total absence of light.
Black ink dots of the short component (dots 13') will represent the
quantity of "minus green" or magenta in the copy, or the total
absence of light. As cyan is blue-green and magenta is blue-red, it
will be realized that the black ink of both components carries
"minus blue" information. It will be understood that the
terminology "minus blue" does not imply that no blue is present in
the copy corresponding to each and every halftone dot, but only
that the separations (in their original negative form) have not
recorded blue, even if present. A halftone dot 12' may actually
represent blue, green, cyan, or black; a halftone dot 13; may
actually represent blue, red, magenta or black. The halftone dots,
in regulating the reflectances from color fields and receiving
surfaces therebetween, merely represent the absence of stimuli.
This is equivalent to projected non-Maxwellian images, wherein the
dark portions are the mere absence of illuminant or stimuli to
greater or less degree depending on the neutral densities of the
projection positives. The same is true for all other 2-color or
3-color pictures made by additive superimposed synthesis, such as
the classical experiments of James Clerk Maxwell. An essential of
my gamut enhancement means is that the halftone dots not be the
mere absence of stimuli, and that the "minus blue" quantity be
replaced with a positive blue quantity of slight and uniform
amount.
My complete gamut enhancement means generally comprises: (a)
Printing my composite image in a partially chromatic blue,
alternatively purple, tone; (b) Using a short separation that has
recorded greens most strongly, but has with less strength also
recorded substantially throughout the blues without being a true
cyan record; (c) Using a long separation that has recorded reds as
well as possible, and has with less strength also recorded
substantially throughout the blues without being a true magenta
record; (d) Using a short stimulus which is either white or of
greenish tint or a fuller green hue; and (e) Using a long stimulus
which is red, or (if the short stimulus is a relatively full value
of green) is either white or of reddish tint. As is generally
preferred, the receiving surface is best made to function as the
short stimulus. By these combinative means blue objects will more
readily be perceived as blue while other colors are not
desaturated, secondary colors dependent on blue will be perceived,
and apparently true black, gray and white will be perceived. I do
not limit practice only to the combinative use of all such
elements, as lesser degrees of enhancement can be had by use of but
some elements, e.g.: the short separation need record no blues or
the long separation need record no blues; one or both stimuli may
be other "warm" and "cool" colors than as recommended.
Although the "dark" ink is everywhere partially chromatic and
uniformly toned with blue (or purple), bluishness becomes manifest
only in proper portions of the picture. This effect, which I call
"induced bluing," is a phenomena probably due to simultaneous
contrast in conjunction with brightness ratios and other effects
active when a picture is viewed rather than isolated spots of light
in a surround. Because my preferred separations are able to
distinguish density-wise between blue and black, halftone dots for
a blue object will not be quite so large or dense as halftone dots
for a black object. The small amount of short and long stimuli not
obscured by these printed halftone dots will give rise to a
sensation of deep yellow or orange, which sensation is sufficient
to bring out the blueness of the immediate dots by phenomena of
simultaneous contrast. The dominance of the local blue sensation
rather than the yellow or orange sensation, is likely due to
non-Maxwellian phenomena together with "constancy" effects. General
reference is made to Wallach, "The Perception of Neutral Colors,"
Scientific American, January 1963, as regards constancy. Similar
reasons may account for the perception of apparently true blacks
and grays even though there is a blue quantity in the image at all
points.
To allow for the use of either a black or gray achromatic or
neutral image as specified by Land, or, as preferred, a partially
chromatic blue-toned or purple-toned image, I have employed the
term "dark" as all inclusive. When the "dark" image is color-toned,
the color-toning need not be so pronounced as to make the image
readily discernible as being a non-neutral tone. Thus my color
toned image affords a practical substitute for black ink when type
matter may be printed along with the multicolor picture. When
purple toning is used, probably only the blue component of the
purple is active in a psychological sense, although no reason for
this is known.
FIG. 22 suggests the general net response of my preferred short
separation, and is not to be confused with transmission of a filter
or filters which may be used to obtain it. The curve is merely
indicative of the general relative amounts of green and blue
recorded and the general spread. In practice it may be approximated
to various degrees, depending on particular
film-illuminant-filter(s) used. Such a short separation may be
obtained by a partial and principal exposure through a green
filter, e.g., Wratten No. 52, No. 57, No. 58 or No. 61, and a
partial and minor exposure through a blue filter, e.g., Wratten No.
48, or through a blue-green filter, e.g., Wratten No. 65. The
combinative successive use of filters is not imperative, but is a
practical expedient in the absence of a single commercial filter of
suitable character. Various other means will be obvious to
phototechnicians, e.g., the combinative simultaneous use of a
blue-green filter and a yellow filter to attenuate the blues. The
use of an orthochromatic or panchromatic emulsion is
understood.
FIG. 23 suggests the general net response of my preferred long
separation, and is not to be confused with the transmission of a
filter or filters which may be used to obtain it. As with my short
separation curve, the curve of response is merely indicative of the
general relative amounts of red and blue recorded and the general
spread, and in practice it may be approximated to various degrees.
Such a separation may be obtained by a partial and principal
exposure through a red filter, e.g., Wratten No. 24 or No. 26, and
a partial and minor exposure through a blue filter, e.g., Wratten
No. 48. As with the short separation, the combinative use of
filters is but a practical expedient, and various other means will
be obvious, e.g., the combinative simultaneous use of a magneta
filter and a yellow filter which will attenuate the blues. It is
understood that a panchromatic emulsion would be used.
My preferred stimuli are deliberately not identical to the
separation colors. Thus, while the separations may each record some
blue, my stimuli preferably have little perceptible blueness. Where
red is specified as a stimulus color, Process Red (magenta) should
be avoided; where green is specified as a stimulus color, Process
Green (cyan) should be avoided; where white is a stimulus it should
not have a bluish cast; and where a cool tint is used the tint
preferably is greenish and not bluish or bluish-green. When color
fields are printed in either red or green on a white or tinted
receiving surface, I do not exclude these color fields from also
being pale and of light value although this is generally not
recommended. When specifying red color fields or a red stimulus I
do not mean to exclude the use of orange-reds, or reds containing a
small amount of blue such as occurs naturally in most red pigments
and dyes.
It will be appreciated that my gamut enhancement means synthesizes
a red-green-blue 3-stimulus system of primaries without resort to a
separate third set of color information in the form of an
additional separation record and additional color fields. In such
respect it is believed unique from Land and from other prior
art.
Land defines his use of the terms "neutral" and "achromatic" in
U.S. Pat. No. 3,003,391 column 1, lines 22-27; in U.S. Pat. No.
3,034,890 column 1, lines 53-59; and in U.S. Pat. No. 3,147,699 by
its being a continuation-in-part of U.S. Pat. No. 3,034,890. In
instances of the specification of U.S. Pat. No. 3,147,699, e.g.,
column 1, line 21, Land uses the phrase "neutral or monochrome"
with reference to his two or more positive separation images. The
only example given of the use of a monochrome image is in the
paragraph beginning column 8, line 31. There he describes only one
of the two component separations as being of color, which color is
intended to be in contrast with its black background and as
luminous and chromatic as possible. Thus, Dr. Land has contemplated
printing one of his pair of separations in a color, e.g., red, but
from the general context of his disclosures it is clear that he has
seen no particular advantage in toning such as I have
described.
It is to be understood that I may, as Land teaches, use other
combinations of stimuli than those I prefer for maximum gamut. For
example, I may use yellow-green paper as the short stimulus and I
may print yellow-orange color fields thereon as my long stimulus,
and one or both of these stimuli may be pale.
My enhancement means may also be applied to projected
non-Maxwellian pictures and other optical displays as described by
Land. The two separations (continuous-tone positive transparencies)
and the stimuli (illuminants or color filters associated therewith)
will, however, be chosen as for my enhanced prints. Accordingly,
the short separation (in its original negative form) may have most
strongly recorded greens and less strongly recorded a broad band of
blues; the long separation (in its original negative form) may have
most strongly recorded reds and less strongly recorded a broad band
of blues. For purposes of projection and the like, the short
stimulus is most suitably a blue-green rather than a green. As
before recommended, the long stimulus may be red. One or the other
of my stimuli may be white or a tint of the fuller color it would
otherwise have. To synthesize my dark partially chromatic printed
composite image the neutral densities of one or both of the
positive transparencies are replaced with deep blue or deep purple
dye, preferably the former. It is not imperative that developed
silver be completely removed. Chemical toning may be employed
instead of dyeing, whereby the toning will appear blue or purple by
transmitted light. The toner might be dichroic, appearing another
color by reflected light.
It is known that the long and short projection positives may be
alternate frames on a cinema film 54, as shown in FIG. 24.
According to my improvement, the "long" frame L can have deep blue
or purple densities 53. To provide a red (as preferred) long
stimulus without need of a colored illuminant or a separate color
filter, frame L may be overprinted with red as indicated by the
vertical shading. The "short" frame S can also have deep blue or
purple densities 53. To provide the short stimulus, e.g.,
blue-green, frames may be overprinted with blue-green as indicated
by the oblique shading. Instead of overprinting my stimulus colors
I may color the film support.
It will be realized that the red on the "long" frame L, by virtue
of its absorbtion, will prevent blue of the densities 53 from
reaching the screen. The densities will thus show as black. If
purple densities were used, only a deep red will reach the screen.
It will also be realized that use of a blue-green dye or ink on the
"short" frame S will only allow blue of densities 53 to reach the
screen, and will absorb red if the densities were purple. Assuming
the use of deep purple densities for all frames, red and blue from
respective "long" and "short" frames will be additively
superimposed on the screen and might become too luminous to
satisfactorily represent shadows. In such case extra deep chromatic
densities must originally be used to compensate. If blue densities
are used for both the "long" and "short" frames, it is irrelevant
that the red on the "long" frames will completely attenuate its
blue densities rendering them as black. Thus it becomes feasible to
similarly process all frames on the film 54, whether to impart blue
densities or purple densities; similar processing is a practical
advantage although not required. For other displays wherein the
separations are each on a separate film, e.g., viewing devices
employing a semi-transparent mirror, one separation may have its
densities in deep blue and the other may have its densities in deep
purple, or one separation may have neutral-tone densities.
Obviously, the subtractive action of stimulus dyes, filters or
illuminants must be kept in mind in determining the particular
chromaticity respective densities are to have.
Instead of using a full blue-green stimulus for the short frames I
may use a blue-green tint, or I may use a pale green stimulus if I
exaggerate the blueness of the densities to allow for attenuation
of the blue which will occur. When a relatively full blue-green is
used as the short stimulus, I may use but a tint of red or no tint
(white light) as my long stimulus.
Having described my invention to the best of my ability, I rely
fully upon the doctrine of equivalents for all variations,
alternatives and derivatives within the scope of the appended
claims, and having features and elements therein regardless of any
additional features or elements.
* * * * *