Note: Descriptions are shown in the official language in which they were submitted.
~g71~3
~he presen-t invention relates to a photographic material
suitable for use in the silver complex diffusion transfer
process.
In photomechanical colour reproduction the information
content of the coloured original is split up in colour
separations, which are used to prepare the proper intermediate
prints that serve as exposure modulators in the exposure of
the photosensitive resist composition of the printing forms.
~he light-sensi-tive material used in the production of
these colour separations is commonly a panchromatic silver
halide emulsion ma-terial. ~ssential in the photomechanical
reproduction is the screening of the separations to transform
the tone values of a continuous tone record in a ~ariety of
black dots, whose area is related to the continuous tone value.
As is known to those skilled in the art screened
separations are used in the exposure of a photoresist material
to produce halftone printing plates, which are made to print
i with a cyan, magenta, yellow and optionally black ink res-
pectively.
Simplified methods of screening of continuous tone images
have become available. ~hese methods involve the use of so-
called contact screens. Such screens are used to produce
screened positives from continuous tone negatives but are
likewise used for the preparation of direct screen separations
from colour transparencies. Years ago the production of
direct screen separations was not much used in practice for
the main reason that it has not been possible to obtain
GV.988 PC~
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1~7~Z3
sufficien-tl~ good tone rendition and colour saturation.
Nowadays direct halftone colour separations are made on pan-
chroma-tic lith-films with recommended colour separation
filters (see ~wald ~red ~oemer, ~he Handbook of Modern Halftone
Photography (1965) published by Perfect-Graphic Arts Supply
Co~pany P.O.Box 62 Demarest, ~.Y. 07627, page 94).
~he processing of halftone images in regular lith
developers re~uires a lot of care and -the investment in
automatic film processors is often required to ensure high P
10quality work. ~herefore it would be interesting to have at
the disposal a direct-screening system in which halftone
separation positives could be obtained from op-tionally pre-
masked colour originals in one single step and with a pro-
cessing system that is rather inexpensive, simple and con-
venient. ~he silver complex diffusion transfer process
(D~R-process) offers such advan-tages bu-t one cannot use any
photographic silver halide material to obtain therewi-th the
desired speed, screen dot quality and exposure latitude
required in the production of screened images.
In order to meet the high quality demands of screened
colour separations with regard to screen dot definition and
tonal reproduction some measures for ensuring dot sharpness
and sufficient exposure latitude have to be taken. ~or
example the very high sharpness demands ask for a strong
reduction of light scattering and counteraction of so-called
halation by light reflexion at the support.
GV~988 PCl - 2 -
~97~3
According to United States Patent Specification 3,091,535
of Clifford ~.Milner, Jr. issued May 28, 1963 which does not
deal with the D~R-process, bleachable antihalation dyes and
pigments for improving the image resolution have been used
in translucent lith films.
~ he use of a bleachable antihalation substance is a
conditio sine qua non for said film material since the overall
colouration due to said substance masks the silver image, which
has -to be viewed against the white background of the trans- -
lucent layer of said material.
In the United States Patent Specification 3,629,054 of
Lodewijk ~elix De Keyser, Joseph Antoine Herbots and Julius
~hiers, issued December 21, 1971 a silver halide emulsion ma-
terial for use in the D~R-process has been described which
comprises a composite film support consisting of a black-
pigmented hydrophobic layer and a white-pigmented hydrophob:ic
layer. ~he material contains in subsequent order a gelatin
silver halide emulsion layer, a gelatin subbing layer, a plas-
ticized hydrophobic cellulose triacetate layer co~taining tita-
nium dioxide and a hydrophobic cellulose triacetate layer con-
taining carbon black. ~he purpose of said layer containing
carbon black is to protect the light-sensitive silver halide
emulsion layer against actinic environmental light during
carrying out the diffusion transfer process in daylight condi-
tions when the light-sensitive material with its emulsion
side in contact with an opaque image-receiving material
GV.988 PCT - ~ -
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~L~97~Z3
leaves the camera. Since the white titanium dioxide layer
during the exposure offers an image-wise light reflection into
the silver halide emulsion la~er an increase in speed is ob-
tained.
~ he incorporation of said white and black pigments in
their respective hydrophobic layers poses serious problems with
regard to brittleness and a sufficient pigment content.
In accordance wi-th the present invention a photographic
; silver halide emulsion material is provided, which is suited
for the production of halftone images of high quality -through
the D~R-process.
~he photographic material according -to the present
invention comprises successively :
(1) a silver halide emulsion layer,
(2) a layer reflecting white light; having a dry coating weight
in the range of 5 g/sq.m to 2C) g/sq.m and containing in an
organic hydrophilic colloid binder white inorganic pigment
particles in such an amount that said layer has a diffuse
transmission density of 0.~0 to 0.50 and a reflection
density of 0.~5 to 0.20,
(3) a subbing layer,
(4) a hydrophobic transparent film support,
(5) a subbing layer~ and
(6) an antihalation layer having a dry coatlng weight in the
range of 4 g/sq.m to 15 g/sq.m and containing dispersed in
an organic hydrophilic colloid binder a non-bleachable
black antihalation substance in such an amount that said
GV.988 PC~ - 4 -
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1~973~23
layer has a diffuse transmission density of at least 2.
~ he "diffuse transmission densi-ty" is measured according to
the requirements of American Standard PH 2. 19 - 1959.
~ y "reflection density" is meant "diffuse reflection
density" which is measured according to the requirements of
American Standard PH 2.17 - 1958.
According to a modified embodiment the antihalation layer
mentioned under (6) is present immediately under the layer
(2) reflecting white light, and the subbing layer (5) is
covered with a clear coating on the basis of an organic
hydrophilic colloid e.g. gelatin, which coating is intended
as anti-curling layer.
r~he thickness of the pigment layer reflecting white light
is preferably in the range of ~ to 6 ~m (micron), e.g. is 4 ~m.
~ he thickness of the black pigment layer is preferably
in the range of 10 to 20 lum e.g. is 15 ~m.
As white inorganic pigment particles titanium dioxides,
which may be of various crystalline forms, are preferably
used. ~he rutile crystalline form gives the highest opacity
for a given weight. However, not only pure titanium dioxides
but likewise so-called coated titanium dioxide pigment particles
may be used. Such means that the white titanium dioxide
pigment has been modified by precipitation thereon of, e.g.,
hydrated aluminium oxide or of hydrated aluminium oxide together
with hydrated silicon dioxide as described, e~g., in the
United States Paten-t Specification 3,928,037 of ~ouis Maria
GV.988 P~ - 5 -
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7~LZ3
De Haes, issued December 23, 1975.
~ he titanium dioxide particles of the layer reflecting
white light have preferably an average grain size in the ran~e
of 50 to 500 nm and are used preferably in the range of 100 %
to 200 % by weight with respect to the hydrophilic binder.
~he hydrophilic binder may be any organic hydrophilic colloid
that can form a water-permeable layer but is preferably gelatin.
Mixtures of gelatin with carbo~ymethylcellulose are very useful.
lhe dispersed non-bleachable antihalation substance is
preferably carbon black e.g. lampblack that has preferably
an average grain size in the range of 10 to 50 nm and is used
preferably in the range of 5 to 40 % by weight with respect
to the hydrophilic binder.
~ he support of the photographic material may be any
conventional transparent hydrophobic film consisting, e.g.,
of a cellulose ester (e.g. cellulo~e triaceka-te, cellulose
nitrate, cellulose acetate butyrate), a vinyl polymer (e.g.
polystyrene and copolymers of styrene) or a polyester,
~preferably a highly polymeric linear polyester of a dicar-
boxylic acid with a dihydric alcohol (e.g. polyethylene
terephthalate)~ ~hese supports in the present invention are
provided at both sides with a subbing layer to improve the
adherence of the hydrophilic binder-pigment coatings.
Suitable subbing layers for that purpose are described,
e.g~, in the United States Patent Specifications 3,495,984
of Johannes Camiel Vanpoecke 9 Lodewijk ~elix De Eeyser and
GV.988 PG~ - 6 -
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11D97~Z3
Andre Jan Conix, 37495,985 of ~odewijk ~elix De Keyser,
Andre Jan Conix and Joseph Antoine ~erbots, both issued
~ebruary 17, 1970, 3,L~34,840 of Bodewijk ~elix De Keyser, Andre
Jan Conix and ~odewijk August Van Dessel, issued March 25,
1969, 3,788,856 of August Jean Van Paesschen, ~ucien Janbaptist
Van Gossum and Jan Josef Priem, issued January 29, 1974 and
United ~ingdom Patent ~pecification 1,234,755 filed September
28, 1967 by Gevaert-Agfa N.V.
~he thickness of the transparent support is preferably
in the range of 0.05 mm to 0.2 mm.
Any type of negatively and positively working silver
halide is suitable for preparing the emulsio~ layer, provided
the silver halide grains are capable of being developed and
complexed in the exposed and non-exposed areas respectively
with the rapidity required in diffusion transfer processes.
Direct-positive silver halide emulsions can be used
comprising silver halide grains that have been fogged, before
or after coating of the emulsion on a support, by an overall
exposure to ac-tinic radiation or preferably by chemical
fogging e.g. by means of reducing agents. Upon image-wise
exposure of the prefogged emulsions the development centres
formed by said fogging are destroyed at the exposed areas and
remain at the unexposed areas. By subsequent development a
direct-positive image is formed. Particularly suitable direct-
positive emulsions are those comprising electron~traps e.g.
compounds acting as electron-acceptors or desensitizers such
GV.988 PC~ - 7 -
~0~7~Z3
as desensitizing dyes which are adsorbed to the surface of
the fogged silver halide grains. Other favourable direct-
positive emulsions are those comprising silver halide grains
containing internal centres promoting the deposition of photo-
lytic silver formed physically or chemically during precipi-
tatio~ of the silver halide grains. ~hese centres form the
electron-traps. Fogging of the silver halide grains con-
taining electron-traps in their interior or electron-acceptors
at their surface preferably occurs by red~ction a~d gold
fogging, more particularly by digestion in the presence of one
or more reducing agents e.g. thiourea dioxide and gold com-
pounds e.g. potassium chloroaurate and auric trichloride or
by digestion at low pAg values in the presence of gold com-
pounds.
More details about fogged direct positive silver halide
emulsions can be found iIl British Patents 723,019 filed
~ebruary 5, 1952 by Gevaert Photo Producten N.V., 1,299,868
filed April 2, 1969 by Agfa-Gevaert A.G. and 1,427,525 filed
July 13, 1972 by Agfa-Gevaert N.V., in US Patents 3,367,778 of
Robert W.Berriman, issued ~ebruary 6, 1968, 3,501,305,
3,501,306, 3, 501, 307, all of B~rnard D.Illingsworth, issued
March 17, 1970, 3,501,310 of Bernard D.Illingsworth and Harry
~.Spencer, issued March 17, 1970, 3,531,290 of Roberta A.
Litzerman, issued September 29, 1970, 3,537,858 of ~lbert
W.Wise, issued No;vember 3, 1970 and 3,963,493 of Willy Joseph
Vanassche, Herman Alberik Pattyn and Hendrik Alfons Borginon
~V .988 PC~ - 8 -
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~09712~:~
issued June 15, 1976.
Another group of direct-positive silver halide emulsion
materials comprises a so-called unfogged direct-positive silver
halide emulsion, which has its sensitivity predominantly in
the interior of the silver ~alide grains. Upon image-wise
exposure of such emulsion a laten-t image forms predominantly
in the in-terior of the silver halide grains. However, the
development of such unfogged direct-positive silver halide
emulsion is carried out under fogging conditions, wherein fog
forms predominantly in the unexposed areas and a positive
silver image results upon development. ~he unfogged, direct-
positive silver halide emulsion material is characterized
thereby that in the exposed parts no silver image is produced
or only one of very poor density upon development by the use
o~ a typical surface developer of the following composition :
p~hydro~yphenylglycine 10 g
sodium carbonate-1-water 100 g
water up to 1000 ml,
whereas a silver image with sufficient density forms if an
internal type developer of the following composition is used :
hydroquinone 15 g
monomethyl-p-aminophenol sulphate 15 g
anhydrous sodium sulphite 50 g
potassium bromide 10 g
sodium hydroxide 25 g
sodium thiosulphate-5-water 20 g
water up to 1000 ml.
G~.988 PC~ - 9 -
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~; . , . .. i,,.... ~ ..
~13197~Z3
~ he selective fogging of the image-wise exposed unfogged
direct-positive emulsion materials can be carried out before
or during development by a treatment with a fogging agent.
Suitable fogging agents are reducing agents such as hydrazine
or substituted hydrazine compounds. Reference may be made -to
US Patent ~pecification 3,227,552 of Keith ~. Whitmore issued
January ~ 1966.
Unfogged direct-positive emulsions are e.g. those showing
defects in the interior of the silver halide grains (ref. US
Patent Specification 2~592,250 of ~dward Philip Davey and
Edward Bowes Knott, issued April 8, 1952) or silver halide
emulsions wi-th covered-grain structure (ref. published German
Patent Application 2,308,239 filed ~ebruary 20, 1973 by
Agfa-Gevaert N.V.).
'~he silver halide of the emulsions used according to the
present inven-tion may be any of the usual silver halides but
preferably substantially consist of silver chloride e.g. at
least 70 mole% of the silver halide is chloride, the remainder
bei~g pre~erably bromide. ~he average grain-size is usually
in the range of 200-300 nm.
In order to obtain a spectral sensitivity over the whole
visible spectrum range (panchromatic sensitivity) the silver
halide is spectrally sensitized with a mixture of known methine
dyes that offer in a proper ratio a spectral sensitivity as
equal as possible for each wavelength between 400 and 700 ~m.
GV~988 PC'l - ~0 -
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~L097~Z3
~ he amount of spectral sensitization dyes present per
mole of silver halide is e.g. from 0.10 to 60 mg.
The hydrophilic colloid used as binder medium for the
silver halide is preferably gelatin.
A suitable coverage of silver halide expressed in g of
silver nitrate per sq.m is in the range of 0.5 g/sg.m to 5g~sq.m.
~ he present invention includes a process for the production
of halftone images, which process comprises the steps of
(1) photographically exposing to a light-image being a line or
screened image a photographic material as defined above,
(2) bringing the emulsion layer side of the exposed photographic
material in contact with an image-receiving layer containing
developing nuclei of an image receptor material in the
presence of a liquid that makes the development of the
exposed silver halide to take place and a silver halide
complexing agent to efEect the trans~er by diEfusion of
silver halide complexes from the photographic material into
the image-receiving la~er to form a visible silver image
therein, and
0 (3) separating the exposed photographic material from the image
receptor material.
In preparing a direct screen image the exposure proceeds
through a contact screen and a continuous tone originalO
When the receptor material contains two image receiving
layers, one at each side of the support e.g. a transparent
film, it does not matter which side is contacted and
G~.988 PC~
1a~97:1Z3
conse~uently any error that may occur in contacting the
receptor material with the emulsion layer of the photographic
material is avoided.
~ hen halftone dot patterns obtained in the image receptor
material by effecting the DTR-process with the photosensitive
material of the present invention are examined with a magni-
fying glass clear and sharp edges of the dots are observed.
In comparison with conventional lith material the obtained
dot image configuration shows an improved sharpness of the dot
edges.
~ or a same density in the dots the absolute amount of
silver is considerably smaller in the images produced according
to the invention than those produced in conventional lith films.
~ he binder of the image receiving layer containing
developing nuclei in dispersed state may be any of the
common hydrophilic binders used i~l the art, e.g. gelatin,
carbox~methylcellulose, gum arabic, sodium alginate, propy-
lene glycol ester of alginic acid, hydrox~ethyl starch,
dextrine, hydroxyethylcellulose, polyvinylpyrrolidone, poly-
styrene sulphonic acid, polyvinyl alcohol, etc.
It is preferred to use nickel sulphide nuclei or silver
sulphide though other development nuclei can be used as well,
e.g. sulphides of heavy metals such as sulphides of antimony,
bismuth, cadmium, cobalt, lead and zinc. Other suitable salts
are selenides, polyselenides, polysulphides, mercaptans and
tin(II) halides. ~he complex salts of lead and zinc sulphides
GV.988 PCl _ 12 -
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are active both alone and when mi~ed with thioacetamide,
dithiobiuret and dithio-oxamide. ~ogged silver halides can
also be used as well as heavy metals themselves in colloidal
form, preferably silver, gold, platinum, palladium and
mercury may be used.
~ he image-receiving layer may be hardened so as to improve
i-ts mechanical strength. Xardening egents for colloid layers
include e.g. formaldehyde, glyoxal, mucochloric acid, and
chrome alum. ~ardening may also be effected by incorporating
a latent hardener in the colloid layer, whereby a hardener
is released at the stage of applying the alkaline processing
liquid.
~urther information on the composition of the image-
receiving layer can be found in "Photographic Silver HalideDiffusion Processes" by André Rott and ~dith Weyde - ~he
Focal Press, London and New York (~972), p. 50-65.
~ or carrying out the silver complex diffusion transfer
process it is common practice to incorporate the developing
agent~ into the light-sensitive silver halide emulsion layer
and/or the image-receiving layer, or other water-permeable
layers adjacent thereto.
In order to ensure a very good keepability, the present
photosensitive material preferably does not contain a
developing substance.
~ he D~R-processing liquid applied in the present invention
is consequently preferably an alkaline liquid containing one or
GV.988 PCT - 13 -
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~a~97~2~3
more developing agents and silver halide complexing compounds.
Suitable developing agents for the exposed silver halide
are, e~g., hydro~uinone and 1-phenyl-3-pyrazolidinone and
p-monomethylaminophenol. ~he development or activating liquid
contains in the process for forming a silver image through the
silver complex diffusion transfer process a silver halide
solvent, e.g., a complexing compound such as an alkali metal
or ammonium thiosulphate or thiocyanate, or ammonia.
Alternatively or in addition such complexing compound may be
present in the image-receiving layer.
~ he exposure of -the light-sensitive material and the
diffusion transfer proceed preferably with, or in the apparatus
commercially available therefor and of which several types have
been described in -the already mentioned book of A.Rott and
E.Weyde.
~ he presen-t invention is illustrated by the following
example. All percentages and ratios are by weight unless
otherwise stated.
~xample
- Preparation of the film material A with one pigment layer con-
taining carbon black
____________________
A washed gelatino silver chlorobromide emulsion (98.2
mole of % chloride and 1.8 mole % of bromide) comprising an
amount of silver halide equivalent to 150 g of silver nitrate
per kg was fogged chemically by addition of potassium chloro-
aurate (1.2 mg per mole of silver halide) at pH 7 and pAg 6
- GV.988 PCl - 14 -
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~7îz3
and by keeping the emulsion at 55C for 3 hours.
400 mg of pinacryptol yellow and 250 mg of the following
desensitizing methine dye of the 2-phenyl-indole class
described in the United States Patent 3,615,610
~3
_ C = CH-CH=C ~ -CH~ I
CH3
were added to the fogged emulsion.
~he pH of the emulsion was lowered to 5 and the pAg raised
to 9.5.
The emulsion was coa-ted at a silver halide coverage
equivalent to 2.75 g of silver nitrate and 1.9 g of gelatin
per sq.m, on a black antihalation layer carried b~ a subbed
polyethylene terephthalate film support having a thickness of
0.1 mm.
~ he black antihalation coating was coated from the following
mixture : -
water 800 ml
35 k aqueous dispersion of lampblack
(average grain size 30 nm) 21 g
gelatin 64 g
12.5 % solution of saponine in a
mixture of ethanol and water
(80/20 by volume) 21 ml
water to make 1 l.
GV.988 PC~ - 15 -
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7123
The coating proceeded at a coverage of 1 litre/17.1 sq.m.
The diffuse transmission density of the black antihalation
la~er was 2.60.
_ Preparation of the film material B with one pigment l~er
containing titanium dioxide.
The silver halide emulsion prepared as described for film
material A was coated at a same coverage on a white pigment
coating, which itself had been applied from the following
coating composition to a subbed polyethylene terephthalate
support having a thickness of 0.1 mm :
water 200 ml
ethanol 110 ml
gelatin 53 g
16 % dispersion of titanium dioxide
(rutile having an average grain size
of 300 nm) in an aqueous gelatin
solution containing 4.3 % of gelatin555 ml
12.5 % aqueous solution of saponine 25 ml
water to make 1 l.
The coating was performed at a coverage of 1 litrej13.3 sq.m
The white pigment coating had a diffuse transmission
density o~ 0.43 and a reflection densi-ty of 0.16. The diffuse
transmission densit~ was measured with a MACB~TH Quanta-~og
Densitometer Model ~D-102 and the reflection density was
measured with the MAGBE~X Quanta-~og Densitometer Model RD-219
(Quanta-~og is a tradename of Macbeth Corporation, ~ewburgh,
NoY~ 12550 U.~.A.).
GV.988 PCT - 16 -
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~og7~23
- Preparation of the ~ilm material C according to the invention
with one pi~ment layer containing titanium dioxide and one
pigment layer containing carbon black.
~ ilm material C was prepared in the same way as material B
with the difference, however, that the rear side of the support
was coated with a black antihalation layer from the following
composition :
water 600 ml
35 % aqueous dispersion of lampblack
(average grain size 30 nm) 27 g
gelatin 100 g
ethanol 73 ml
12.5 % aqueous solution of saponine 13.5 ml
4 % aqueous solution of formaldehyde11 ml
water to make 1 l.
~ he coating was performed at a coverage of 1 litre/14.5
sq.m.
~ he diffuse transmission density of the black antihalation
layer was 3.00.
~ hese film materials were used under the same conditions
in the ~R-process in combination with an image-receiving
material prepared by coating a subbed polyethylene
terephthalate film with the following coating composition :
water 800 ml
gelatin 62 g
aqueous dispersion of 0.20 % of colloidal
silver sulphide and 11.6 % of gelatin 33 ml
GV.988 PC~ - 17 -
~L~97~:3
12.5 % solu-tion of saponine in a mixture
of ethanol and water 80/20 by volume 35 ml
20 % aqueous formaldehyde solution 10 ml
water to make 1 l
~he coating was per~ormed in such a way that after drying
at 50C a layer having a dry weight of 54.~ g per sq.m was
obtained.
~or compara-tive de-termina-tion of the exposure latitude
of the above materials A, B, and a these materials were exposed
in contact under the same conditions through superposed
wedges, one of which being a screened wedge having in super-
position thereon but turned over an angle of 90 the other wedge,
which is a continuous tone step wedge having a constant of 0.15.
~he identically exposed ma-terials A, B, and C were D~R-
processed in contact with the above receptor material b~ means
of a developer solution containing the following ingredients :
water ~00 ml
sodium hydroxide 10 g
hydroquinone 10 g
1-phen~1-3-pyrazolidinone 1.5 g
sodium thiosulphate 5 g
potassium bromide 0.5 g
sodium sulphite 50 g
water to make 1 l.
In each step area of the prints obtained the point P
corresponding with 0 % dot value (no dots recognizable with a
. GV.988 PC~ - 18 -
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magnifying glass-enlargement factor 50x) and the point Q
corresponding with 100 % dot value (total blackening, no
screen dots separately recognizable) were determined.
In order to illustrate the exposure latitude of said
materials A, B and C the shift (S) (logarithmic values to the
base 10 in the ordinate) of point P and point Q with respect
to their position on the original screen wedge as a function
of increasing exposure (rela-tive log E in the absciss) is given
in the accompan~ing figures 1 to 3.
~he shift (S) stands for a change of the screen range at
the side of point P and Q respectively as a function of relative
log exposure.
Each of the figures therefore contains two curves, one
(curve P) showing the shift of point P (corresponding with 0 %
dot value) and one (curve Q) showing the shift of point Q
(corresponding with 100 % dot value) both depending on rel. log E.
From figures 1, 2, and 3 relating to materials A, ~, and
C respectively it can be learned that material A possesses the
greatest exposure latitude, that material B through its large
shift of point Q has but a poor exposure latitude, and that
material C according to the present invention shows an
unexpected relatively low shift for both points, which makes
the material particularly useful for the production of
separation images according to the D~R-process.
Besides, the relative speed values of the materials A, B7
and C in the present D~R imaging have been determined at optical
GV.988 PC~ - 19 -
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: .
~97~L23
density 1.00. ~hese speed values expressed as relative log
values were 1.97, 1.52, and ~.55 for the materials A, B, and
C respectivel~. ~he higher the log value number, the lower
the speed. A decrease of 0~3 corresponds with a doubling
of speed.
As a result of the high speed value of material C and of
its broad exposure latitude, this material C is especially
suited for camera reproduction of halftone images such as
screened colour separation images.
GV.988 PC~ - 20 -
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