Note: Descriptions are shown in the official language in which they were submitted.
33i~
This invention re:Lates generaLly to halftone printing and more
particularly to a novel halftQne printing process which can be readily prac-
ticed in a simple and economical manner without requiring skilled operators
to produce printed impressions having density ranges substantially equal to
those of photographs. The invention also relates to advanced halftone offset
machine plated or press plates which can be produced from halftone positives
or halftone negatives for offset, letterpress, or gravure printing, and which
produce printed impressions of density curves substantially corresponding to
those of photographs.
Heretofore, the so-called "conventional" process, wherein variations
in density are produced by the sizes of the halftone dots, has been generally
` ` practiced as a halftone printing process. In representing tone in this con-
ventional process, however, the regions in the vicinity of the smallest dots
and the largest dots of the halftone dots are often neglected with respect to
`~ the techniques of photography and printing, and the highlight parts (small
dot parts) and shadow parts (large dot parts) of the printed matter tend to
become flat, whereby the maximum density cannot be elevated to that of a photo-
graph.
For the purpose of overcoming this difficulty, the so-called "duotone"
process was developed. By this duotone process, the halftone dot angle is
changed so as to prevent moiré from being produced. By this process, however,
in spite of some improvement in the highlight parts of the printed matter3
~ density gradation for representing the shadow parts, which occupy a wide
- density range, is deficient, and it is not possible to fully represent tone.
Another known process is the complementary color process, in which
color density is corrected by superimposing a light-color plate. By this
process, also, while the tone of the color is somewhat corrected~ density
gradation for representing the shadow parts of the printed matter is deficient
- and is not sufficient for representing tone.
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In this representation of t~ne by combination with ~ight color, it
is very difficult to predict beforehand the tone of the finished printed im-
pression. For this reason, this is often carried out in the proof stage, and
several dot angles which will not give rise to moire must be determined. At
the same time, because of the difficulty of the work and the complex nature of
`~ the work process, an extremely high degree of technical skill is required.
Moreover, work over a long period is necessary, and much material must also
be used.
i It would appear that representation of the shadow part on the
printed matter occupying a wide density range by expanding the density range
is possible by increasing the ink film thickness. However, as a result of a
general behavior of a printing ink, which is one kind of fluid, when the ink
film thickness, that is, the solid density, is reduced, the dimensions of the
dots produced by the transfer of the ink tend to undergo an overall shrinkage,
whereas, when the ink film thickness, that is, the solid density, is increased,
the sizes of the dots produced by the ink transfer tend to undergo an overall
increase .
Consequently, when the solid density is lowered to reduce the si3e of
the dots, the entire impression becomes of light color~ and the tone becomes weakO
Conversely, when the solid density is raised to increase the siæe of the dots,
the entire impression becomes dark, and the tone becomes strong. As a result~
` the dot gain approaches a fill-in state, or fill in occurs, giving rise to
blotching of the print~ loss of the tone render-ability~ and overall darkening.
The tone renderability for every percentage of dot density is
influenced by the ink film thickness, that is, the solid density, and the ;
reproduction of the overall tone is determined by the accuracy of reproduci-
bility of the individual dots. That is~ the to~e reproducibility of a printed
impression depends on the accuracy of reproducibility of the size of the dots
and the thickness of the ink film transferred onto these dots. This is true
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,
not only with monochrome processes but also with color processes.
It is an object of this invention to provide a halftone printing
process by which the density range of the conventional printed impression is
L enlarged, and printed impressions substantially identical to photographs can
be obtained.
More specifically, an object of the invention is to provide a half-
tone printing process by which printed impressions wherein the density tone
gradation is rich, and the tone is substantially the same as that of a photo-
graph can be printed in an efficient and simple manner.
It is another object of this invention to provide a set of halftone
offset press plates capable of printing, in a simple manner with high work
efficiency, printed matter of rich density gradation and excellent tone similar
- to that of photographs.
The halftone printing process according to this invention comprises
a first process step in which a first impression is printed in entirety with
a solid density of good renderability from the middle-tone part to the light~
tone part in an original and at least one second process step in which
- printing is carried out in superposition over the first impression with a
printing plate lightly and supplementarily expressing only the parts of high
dot area %J also referred to hereinafter as dot density, of said origlnal.
The apparatus of the invention consists of a set of halftone offset ;
press plates comprising a first plate which has been contact photoprinted with
a screened film made from a transparent or reflecting original and at least a
second plate adapted to express somewhat lightly and supplementarily only
-
; parts of high dot area % of said first plate, said plates being used to
print superposed impressions to form a final printed matter.
By the practice of the halftone printing process according to this
-~ invention~ printing is carried out in entirety in a manner to make possible
.
~ faithful expression of density tone gradation from middle parts through light
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parts, which has heretofore been possible, by means of an ordinary printing
plate produced by contact printing a halftone screened film made from a trans-
parent or reflection original copy, and superposed printing is carried out
with a printing plate in which only the parts of high dot density, which have
discontinuity or poor rendering, are further lightly and supplementarily ex-
pressed, whereby the density tone gradation of only the parts of high dot
density can be compensated for without disturbing the tone from the middle
parts through the bright parts.
Since this supplementary or compensating printing is carried out
with almost no variation of the solid density and with the use of a printing
plate in which only the parts of high dot density are lightly and supplement-
arily expressed, that is, a plate in which the area of the dots is reduced in
comparison with that of a plate for overall printing, printing is possible
without density curve discontinuity, moreover, with only the simple procedure
of matching the register marks, and without the occurrence of moire'. Thus, an
advantageous feature of this invention is that, since moire'is prevented from
occurring excellent impressions can be obtained without the necessity of
printing with varied dot angle.
In the use of the abovementioned set of press plates, a first im-
pression is printed by means of the first plate and then at least one impression
is printed by means of the second plate in superposition over the first
impression only at the parts thereof ranging from middle-tone parts through
shadow parts, more specifically, parts of densities above 50~. Moreover,
since the corresponding dot parts of the second plate are somewhat lightly and
supplementarily expressed, the density range is expanded in the shadow parts
of the printed matter, and a printed matter of good tone can be printed by
merely aligning the register marks and printing ~th ink of the same density.
For this reason, there is no necessity for adjustment of dot angle of screen
in order to prevent moire'. Furthermore, special skills such as that for re-
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- ~8~338
touching are not necessary, and printed matter of a width of density gradation
and expanse of the density region of the same order as those of phokographs
can be simply and econon~cally obtained, e~cellent renderability being posi-
tively attainable at the same time.
Other advanatages and features will be more clearly apparent ~rom
the following detailed description.
~ In the drawings:
``` Figure 1 is a graph indicating variation of density relative to
screen dot density or screen percentage (%) of printed matter printed by the ~ ;
process and plates of this invention; and ~ -
Figure 2 is a graph indicating variation of density relative to
- screen dot density or screen percentage (%) of printed matter printed by
plates after the second plate.
In accordance with this invention, in a first printing step, printing
is first carried out with solid density such as to obtain a printed matter in
which the middle part to the light part, that iS9 the part of a dot density
less than 50 percent, is as close as possible to at least the theoretical value
of the density curve. The plate (first plate) used in this step must not be
one in which 10% of the dots appear to have disappeared, and 90% are filled in
as in an ordinary plate, but must be one which has been faithfully reproduced.
- Preferably, the printing is carried out in a manner such that the parts of
` dot density less than 80% are faithfully reproduced. -
These techniques have been established in the prior art and may be
- practiced by ordinary methods.
:-~
In the case where the number of screen lines is relatively coarse,
and it is desired to impart forceful intensity in the region from the middle
- part through the dark part, an increase in the size of the dots up to appro~i-
mately ~20% is permissible.
In a second printing step following the abovedescribed first printing
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~8~33t3
step, printing is carried out by means of a second pla~e in which only the
parts of dot density above 50%, preferably above 70% and more preferably only
the parts of` high dot density above 90% are supplementarily expressed. A
plate which is supplemen~arily expressecl with a dot density above any poin~
?~ as a starting point may be used provided that the parts are of this dot de~sity
above 50%.
In this second printing step, an impression with intensity can be
prlnted by superimposed impressions with a printing plate in which only the
parts above 70% are supplementarily expressed, and the density range can be
expanded to that similar to a photograph with a printing plate in which only
the parts above 90% are supplementarily expressed.
In this second printing step, furthermore, the printed dots are
somewhat smaller in area (i.e., expressed somewhat lightly) than the dots in
the first printing step in the corresponding parts, and, for this reason, a
break or discontinuity in the density curve is not observable. Furthermore,
it becomes possible to print with the ink density maintained constant.
While the first press plate of this invention is of a construction
similar to that of a press plate of the ordinary conventional process, it
differs in that it is a plate wherein the parts thereof of high dot density,
e.g., over 90%, and parts thereof of low dot density, e.g., less than 10%, are
not neglected but are expressed. Ordinarily, since parts of a film screen of
dot density over 90~ are difficult to express on the printed matter~ it is a
common practice not to form dots in these partsO In accordance with this
invention, however, formation of solid parts of this character are avoided as
much as possible in the first plate.
The selection of the plate material of this first plate is not limited
in this invention, it being possible to use plates for ~inc plates, aluminum
plates, PS plates, deep-etch plates, and the like. In the case where the
first plate is to be produced from a screen positive film, a plate material
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for screen positive use is used. For producing the ~irst plate from a screen
negative film, a plate material for screen negative use is used.~ Accordingly,
in the preparation of the press plates (including the first and second plates
and others,if necessary) according to this invention, either a positive or a
negative screen film can be used.
The second plate differs from the first plate in that it is a plate
somewhat lightly and supplementarily expressing only the parts of high dot
,- ~
density of the first plate. That is, this second plate prints only the middle-
tone parts to be shadow parts in the printed matter. When the first and second
plates are compared, it is observed that the parts in ~hich dots are formed of
the second plate are more restricted than those of the first plate.
; More than two second printing steps can be carried out. For example,
-~ in the case of two second printing steps, the second impression of the second
- printing step is made with a plate on which is lightly expressed only the part
` of dot density higher than that expressed at the time of the first impression
of the second printing step. For example, in the case where the first impres-
;- sion of the second step has been made with a dot density higher than 70% as ,
. . .
the starting point, the second impression can be made with a dot density
~ higher than 80% as the starting point. In the case of more than 90% as the
- 20 starting point in the first impression, the second impression can be made with
~ more than 95% as the starting point.
- Use of two or more of the second printing step in this manner pro-
, . . .
duces a greater intensity, and printing of a density range equivalent to that
of a photograph can be accomplished.
It is not necessary in all cases to use two or more second printing
steps as described above. For example, when a solid density of 1.5 or higher
- value is produced in the first printing step, and a solid density of the same
or higher value is produced in the second printing step, a very good printed
matter is obtained, although it is not so good as compared with the case where
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~84~8
' two or more second printing steps are used.
In this case, furthermore7 by using a plate which lightly expresses
the dots in only the parts above 80% in the second printing step and increasing
the solid density thereby to produce in the maximum density part a density
close to that in the case where two or more second printing steps are used, a
result which is closer to the theoretical value than to the density curve of
- a paper print photograph is obtained.
Thus, the number of second printing steps and the values of the
solid density and the dot density to be used as the starting point in the
supplementary expression of the plate are determined by the character and use
of the printed material to be thus obtained and are not basically limited in
the practice of this invention.
- ; For example~ when-the difficulties of trapping and offsetting are
considered, a method wherein two or more second printing steps are not used
in a multicolor press or a web offset printing press may be a desirable mode
~- of practice in that it affords economy in labor cost, materials cost, and
production cost and speed up of the production process.
One or more plates similar to the second plate can be usedO Tha*
is, for example, a third plate in which only the parts of high dot density of
the dot formed parts of the second plate are expressed somewhat more lightly
than in the second plate can be used. In the case where parts of dot densi-
- ties above 70% are expressed on the second plate, the third plate is prefer-
ably one on which parts of dot densities above 80% are expressed more lightly
than on the second plate. In this case, the printed matter will become one
having a forceful appearance.
In the case where the second plate expresses the parts of dot densi- -
- ties above 90%, a third plate expressing only parts of dot densities above 95%
more lightly than the second plate can be used.
The second plate~ third plate, etc., can elevate the density from
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the middle-tone parts to the dark parts of the printed matter ~ithout disturb-
ing the expression of the tone of the entire printed matter, particularly from
the middle-tone parts to be light parts, in conventional offset printing, in
~hich the density cannot be elevated l~ithout disturbance of the tone due to
dot gain of the printed matter. The reason for this is that the second plate,
third plate, etc., express supplementarily only the parts of high dot density
which parts, moreover, are lightly expressed.
The method of producing the press plates of this invention, basically,
is not ljmited. For example, on the first plate, a halftone negative or a
halftone positive is produced from a transparent or reflecting original by
applying a screen to a negative or a positive film similarly as in the ordin-
- ary method. Any film can be used provided that it is one for screen use
- Furthermore,t~e kind of screen, basically, is not limited. For example, a
con~act screen or a glass screen can be used. Screens of 65~ 85, 100, 110,
120, 133, 150, 175, 200, 250, 300, etc., lines per 2.54 cm. (1 inch) can be
used depending on the necessity.
` For exposure, a flash is additionally used, care being taken to
obtain all dots from minimum dots to maximum dots without om~ssion. The dots
particularly in the shadow parts in the halftone positive, that is, dots above
90%, must not be filled in. In the case of a halftone negative, conversely to
the case of a halftone positive, the film is expressed without disappearance
of the highlight parts below 10~.
Photoprinting is carried out by placing in a printing frame a plate
blank which has been gr~ined and has been sensitized with the film and pri~ g
by vacuum contact. For the light source, an ordinary arc lamp, a mercury lamp
- or the like is used.
Each of the plates after the second plate or third plate can also be
produced by making a screened film, similarly as in the case of the first plate,from a transparent or reflecting original and contact printing on a plate blank.
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33t3
It is necessary, ho~iever, that this screened film be one which lightly and
" supplementarily expresses only the middle-tone parts to the dark parts (pre-
ferably dot densities above 50~ with a halftone positive and dot densities
below 5~ Wit~l a halftone negative) on the printed matter of the plate subse-
quent to the first plate or the second plate.
In the case of a halftone positive from a screened film made from a
transparent or a reflecting original, the plate after the second or third
plate can be produced by varying the exposure time only on parts of high dot
density (parts of low dot density in the case of a halftone negative) in the
lQ scraening process step to produce the screened film and carrying out printed
therewith. `
, Furthermore, pre-ss plates of a number of steps can also be produced
from a screened film made from a transparent or reflecting original by direct
contact printing by varying the exposure time. By using an arc lamp, a mercury
lamp or the like as the light source, and effecting control with the exposure
time, light distance and the developing time, it is possible to produce the
plates after the second plate or the third plate for supplementarily expressing
only the parts of high dot density of the printed mat~er.
In each of these methods of producing the plates, a halftone positive~
~o or a halftone negative for, for example, offset, letterpress, or gravure can
be used.
The sequence in which the first and second printing steps are carried
; out can be selected at will.
For example, the printing may be carried out from the third plate or
it may be carried out from the second plate, the printing order being select-
able at will.
The halftone printing process according to this invention is applic-
able not only to offset printing but also to various other halftone printing
processes such as letterpress printing and gravure printing, and the resulting
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printed matter cannot only be used ~s an ordinary printed matter but also be
substituted for a real photograph by printing on paper. ~or example, the
resulting printed matter can be used as a transparency for display by illumi~
nation from the reverse side, IYhich was not possible with a conventional
printed matter.
; In accordance with this invent;ion, it is possible to supplementarily
express up to the darkest parts without disturbing the tone of the entire
impression, to expand the density range, to attain the density of an original
` paper print photograph (reflection orginal copy) and, in some cases, to attain
lo or exceed the highest density of an original positive film (transparent COpy)
- More specifically, solid densities of 1.30 to 1.65 with yellow, 2.05 to 2.17
with magenta, 2.05 to 2.17 with cyan, 2.10 to 2.30 with black, and 2~30 compos-
itely can be attained or even exceeded in some cases, and densities measured as
transparent densities can reach or exceed in some cases the highest density of
an original positive film and can exceed the highest density of an original
paper print photograph.
Furthermore, in the second printing step, the density of the parts
in which moire'can occur is very low, and, moreover, the dot area is smaller
than that of the corresponding parts in the first prin~ing step. Therefor~,
by accurately matching register marks, the occurrence of moire-can be prevented. -
In parts where the dot density is higher than 90~ in the first printing step,
no moire, whatsoever, is observable.
- By the practice of this invention, the density curves of the tones to
be reproduced can be varied almost at will, and impressions exactly as desired
can be obtainedO
` In order to indicate more fully the nature and utility of this in-
vention, the following examples of practice thereof are set forth, it being
understood that these examples are presented as being illustrative only and
are not intended to limit the scope of the invention.
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:~89L~3~
Examples
Printing impressions were made by the process of this invention,
and the densities ~rith respect to their dot densities were measured. Each
printing plate was made by using a 150/2.54-cm. screen. The results were as
shown in the follo~ring table.
In the following table, the reference character A designates an
impression or printed matter in the case wherein it is printed by the above
described first printing step, with the first plate, and the reference
characters B, C7 and D designate impressions or printed matter in the case
wherein they are printed by the abovedescribed second printing process, with s
second, third and fourth plates respectively. Furthermore, the combined
designation A+B, for example, denotes an Lmpression or printed matter printed
by printing B in superposition on A. In other words A+B is printed super-
posedly by the first and second plates. The same applies to other combined
designations A~C, A~BtC, A~C~D, and B~C.
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33~3
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a) I~ ~ o ~, ~D ~5, 0 G~) r~ O a~ cc) ~ 0 o ,~ 9 ~ ~ O
,~, a ,_i,i ,; ,; ,;,;,; ,; ,~ ,j,j,; ~ C`l C`; C`i r-i r;r;ri r; r;r-i r~ ~i ri ri ri ri
d~ ~ r~ ~ cn o a~ ~ U) 1~ t- ~n ,~ o o r~) d ~ o o u) ~ ,~ u) oo ,~ rl C-
, i ri ri ri ri ri ri r;~i ri ri ri ~ C`l C~ i r; ri ri ri ri ri ri O ri ~--1 ri ri ri
~ ~ 9 1~ C~ r~ 1~ 0rl ~) r~U) 1~ 0 0 ~C) 5) r~ O ~ ~ O d- U) C~ 10
O ~ ~ ~ a o o o ~ ~~ ~ ~ ~ r~
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r~ O O O O O O OO O O OO O O O O O O O O O O O O O O O
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o ~ Do ~
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i, O O O O O O O OO O O OO O O O O O O O O O O
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O O O O O O O O O O O O O O O O O O O O O O O
~ o o o o o o o oo o o oo o o o o o o o o o o
f. ~ O C~i r~ r1 r~ r~ r~ r~ r~ l C`l C~l C`l C~ l rl r~ r~ r~ r~ ~I r~
,.- O O O O O O O OO O O OO O O O O O O O O O O
~ r~ Cr~ r~ r~ Cr~ Cr~ r~ ~ r~ ~ r~ r~ r~ ~ r~ ~I (r~ r~ Cr~ Cr~ r~ r1 r
. ' O O O O O O O OO O O OO O O C~ O O O O O O O
U~ o o o o o o o o o o o o o o o o o o o o o o o
OooO ~ooO Oooo oooo oooo ooo
o o o o o o o o o o o o o o o o o o o o o o o
O o o o o o o o o o o o o o o o o o o o o o o
.
r~ r;~ r~ r~ r~ ~ r~
p
h f~ 1~
p ~ ¢ ~¢ ~ ¢
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r~ ~ r~ r~ r~ r1 C~ f.
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:L~8~338
~hen these results are plotted as a graphical representation, they
become as shown in Figure 1. ~y the practice of the process and by the use
of the press plates according to this invention, the density range is expanded
in comparison with that heretofore attainable, and the density curve is simi-
- lar in shape to that of the theoretical density curve of the positive film,
from ~hich it is apparent that the renderability is better than that known
} heretofore. In this graph, the shaded region represents the middle-tone parts
ofthe printed matter or impression, and ~A+C+D) printed with the use of the
~` press plates of the invention exhibits a dot gain which is less than that of
t 10 conventional printing, indicating that good printing has been achieved. In
particular (A+C~D) has no dot gain in the middle parts in comparison with
those of conventional printing.
Figure 2 is a graph showing density curves of impressions or printed ~ ;
matter printed bytheprinting of only the second printing step of this in-
r vention. There are shown the density curves for plates B and C together with
the curve for plates B~C. From this5 it will be apparent that B has been
printed with 63% as the starting point, C with 80%, and D with 95~.
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