FIELD OF THE INVENTION
[0001] The present invention relates to a combination of photosensitive elements for use
in radiography and, more in particular, to a combination of a fluorescent phosphor
screen pair and a double-side coated silver halide radiographic element for use in
industrial or medical radiography.
BACKGROUND OF THE INVENTION
[0002] In radiography, and particularly in medical radiography, light-sensitive elements
having silver halide emulsion layers coated on both faces of a transparent support
(called double-side coated silver halide elements) are used. Said double coated silver
halide elements are generally used in combination with fluorescent phosphor screens
in order to reduce the X radiation exposure necessary to obtain the required image.
Generally, one fluorescent phosphor screen is used in association with each silver
halide emulsion layer of the double coated element. The silver halide emulsions used
in the double coated element are sensitized to a region of the electromagnetic spectrum
corresponding to the wave length of the light emitted by the phosphor materials used
in the fluorescent phosphor screens, thus obtaining a significant amplification factor.
[0003] The quality of the image obtained upon X radiation exposure of said screen pair and
double coated silver halide element combination and development of said double coated
silver halide element is negatively affected by crossover exposure. Crossover exposure,
which causes a reduction in image sharpness, occurs in double coated silver halide
elements when light emitted by one fluorescent phosphor screen passes through the
adjacent silver halide emulsion layer and, the light having been spread by the support,
imagewise exposes the silver halide emulsion layer on the opposite face of the support.
[0004] The crossover exposure causes poor definition even if light-sensitive elements are
used which employ reduced silver halide coverages to lower the costs or increase the
processing speed of the element. In fact, the decrease of the emulsion turbidity
increases the amount of light available for crossover and therefore worsens the image.
[0005] To reduce the crossover exposure, dyes or pigments can be used within the radiographic
element. The absorption of said dyes or pigments is in a region of the electromagnetic
spectrum corresponding to the wavelength of the light emitted by the fluorescent phosphor
screens. The dyes or pigments absorb some of the light emitted by the fluorescent
phosphor screen so that imaging of a silver halide emulsion layer by the opposite
screen is reduced by absorbance of the light from the opposite screen by the anticrossover
dyes or pigments. These dyes or pigments are eliminated during the photographic developing,
fixing and washing process of the exposed material; they can be for instance washed
away or, more preferably, bleached while processing the radiographic element.
[0006] The dyes can be incorporated in any layer of the light-sensitive element: in the
emulsion layer, in an intermediate layer between the emulsion and the base, or in
the subbing layer of the support base. It is preferred to incorporate the dyes in
a layer different from that containing the emulsion to avoid possible desensitization
phenomena. Since 1978, Minnesota Mining and Manufacturing Company has sold a radiographic
element under the name of 3M Trimax
TM Type XUD X-Ray Film to be used in combination with 3M Trimax
TM Intensifying Screens. Such radiographic element comprises a transparent polyester
base, each surface of which has a silver halide emulsion layer sensitized to the
light emitted by the screens. Between the emulsion and the base is a gelatin layer
containing water-soluble acid dyes, which dyes can be decolorized during processing
and have an absorption in a region of the electromagnetic spectrum corresponding to
the wavelength of the light emitted by the screens and of the spectral sensitivity
of the emulsion. The dyes are anchored in the layer by means of a basic mordant consisting
of polyvinylpyridine.
[0007] In the practical solution of reducing the crossover exposure by using a mordanted
dye layer (as described for instance in the European Patent Application 101,295),
some problems are created which up to now have not yet been solved properly. In fact,
the improvement of image definition involves not only a natural decrease of the light-sensitive
element sensitivity caused by the absorption of the transmitted light which otherwise
would take part in the formation of a part of the image, but also the possibility
of desensitization phenomena due to the migration of dye not firmly mordanted in the
silver halide emulsion layer. There is also a problem with residual stain even after
processing, the retention of significant quantities of thiosulfate from the fixing
bath which causes image yellowing upon long-time storage on shelf, and lengthening
of the drying times after processing because of element thickening.
[0008] Other approaches have been suggested to reduce crossover, as reported hereinafter.
[0009] US Patent 3,923,515 discloses a relatively lower speed silver halide emulsion between
the support and a higher speed silver halide emulsion layer to reduce crossover.
[0010] US Patent 4,639,411 discloses a photographic element, to be used with blue emitting
intensifying screens,having reduced crossover, said element comprising coated on both
sides of a transparent support a blue sensitive silver halide emulsion layer and,
interposed between the support and the emulsion layer, a blue absorbing layer comprising
bright yellow silver iodide grains of a specific crystal structure.
[0011] Japanese Patent Application 62-52546 discloses a radiographic element of improved
image quality comprising coated on both sides of a transparent support a light sensitive
silver halide emulsion layer and, interposed between the support and the emulsion
layer, a layer containing water insoluble metal salt particles having adsorbed on
their surface a dye. Said dye has a maximum absorption within the range of ± 20 nm
of the maximum absorption of said silver halide and corresponds to the light emitted
by intensifying screens. Silver halides are disclosed as preferred metal salt particles.
[0012] Japanese Patent Application 62-99748 discloses a radiographic element of improved
image quality comprising coated on both sides of a transparent support a light-sensitive
silver halide emulsion layer and, interposed between the support and the emulsion
layer, a silver halide emulsion layer having substantially no light-sensitivity.
[0013] The approaches of using light-insensitive silver halide layers as anticrossover layers
interposed between the support and the light-sensitive silver halide emulsion layers,
although preferred to using dyes or pigments, encounter some problems such as the
increase of silver coverage and bad bleaching characteristics in photographic processing
(residual stain).
[0014] The following are additional documents illustrating the state of the art.
[0015] BE 757,815 discloses a combination of a silver halide element and an intensifying
screen comprising a fluorescent compound emitting light of wavelength less than 410
nm.
[0016] US 4,130,428 discloses a combination of two fluorescent screens and a double coated
silver halide element wherein the maximum emission of the screens is in the wavelength
range of 450-570 nm and silver halide layers are sensitive to light in the same wavelength
range.
[0017] US 3,795,814, 4,070,583 and GB 2,119,396 disclose rare earth oxyhalide phosphors
activated with terbium and/or thulium employed in fluorescent screens having UV emission.
[0018] FR 2,264,306 discloses a combination of a silver halide element and fluorescent screen
comprising a rare earth activated rare earth oxyhalide phosphor having it maximum
emission in the wavelength range of 400-500 nm.
[0019] EP 88,820 discloses a radiographic fluorescent screen comprising a first blue emitting
phosphor layer and a second green emitting phosphor layer to be combined with a silver
halide element having spectral sensitivity in the blue-green region ("ortho-type"
elements).
[0020] JP 60175-000 discloses a combination of a double coated silver halide element and
a screen pair wherein the fluorescent layers of the two screens have different wavelength
region emissions and each screen comprises an organic dye to absorb the light emitted
by the opposite screen.
[0021] EP 232,888 discloses a combination of a double coated silver halide element and
a pair of front and back intensifying screens wherein said front and back screens,
emitting light in the same wavelength region, have different modulation transfer
factors to be used in low energy radiography.
[0022] US 4,480,024 discloses the combination of a silver halide photothermographic element
and a rare-earth intensifying screen which are uniquely adapted to one another for
the purpose of industrial radiographic imaging. The photothermographic element is
dye-sensitized to the spectral emission of the screen and the combination of screen
and element has an amplification factor greater or equal to at least 50. According
to this invention preferably a single screen is used in combination with a single-side
coated photothermographic element , or double screens with either single-side or a
double-side coated photothermographic elements, the latter without any significant
benefit and at increased cost of film.
SUMMARY OF THE INVENTION
[0023] The present invention provides a combination of a pair of radiographic fluorescent
screens and a double coated silver halide radiographic element. Each screen is arranged
adjacent to each silver halide layer and each screen is capable of imagewise emitting
radiation to which the adjacent silver halide layer is sensitive when imagewise exposed
to X radiation. The combination is characterized in that one fluorescent screen emits
a first radiation in a first wavelength region of the electromagnetic spectrum and
the other fluorescent screen emits a second radiation in a second wavelength region
of the electromagnetic spectrum, and each silver halide layer is substantially insensitive
to the radiation emitted by the opposite screen.
[0024] In particular, the present invention provides for a combination of a pair of front
and back radiographic fluorescent screens and a double coated silver halide radiographic
element, wherein the first radiation emitted by said front screen has a wavelength
which differs from the second radiation emitted by said back screen by at least 50
nm, and each silver halide layer is substantially insensitive to the radiation emitted
by the opposite screen.
[0025] More in particular, the present invention provides for a combination of a pair of
front and back radiographic fluorescent screens and a double coated silver halide
radiographic element, wherein said front screen comprises a non-actinic radiation,
preferably green radiation, emitting phosphor and is arranged adjacent to a front
silver halide layer comprising a silver halide emulsion spectrally sensitized to the
light emitted by said front screen, and said back screen comprises an actinic radiation,
preferably UV radiation, emitting phosphor and is arranged adjacent to a back silver
halide layer comprising a silver halide emulsion insensitized to the visually observable
regions of the electromagnetic spectrum.
[0026] The combination of screen pair and double coated silver halide element for use in
radiography according to the present invention provides images having superior image
quality, particularly less crossover, as compared to conventional radiographic screen
pair and double silver halide element combinations without causing negative effects,
such as significant loss of sensitivity, residual stain, image instability upon storage,
excessive element thickening and increased silver coverage. The combination may
be used in industrial or medical radiography.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027]
Figure 1 is a schematic diagram of a radiographic element and screen pair combination
of the present invention.
Figures 2 and 4 are graphs illustrating emission spectra of radiographic fluorescent
screens of the present invention.
Figures 3 and 5 are graphs illustrating spectral sensitivity of a double-side coated
silver halide radiographic element of the present invention.
Figures 6 and 7 are graphs illustrating sharpness and granularity versus sensitivity
of radiographic double coated silver halide element and screen pair combinations.
DETAILED DESCRIPTION OF THE INVENTION
[0028] The present invention will be now described in detail.
[0029] Figure 1 shows in greater detail a combination of the screen pair and the double
silver halide element of this invention. The combination comprises three separate
photosensitive elements: a double coated silver halide radiographic element 10, a
front screen 21 and a back screen 20.
[0030] As shown, the double coated silver halide radiographic element 10 comprises a support
11 and coated on its opposite faces are the subbing layers 12 and 13. A front silver
halide emulsion layer 15 is coated over the subbing layer 13 and a back silver halide
emulsion layer 14 is coated over the subbing layer 12 on the opposite face of the
support. Protective layers 16 and 17 are coated over the silver halide emulsion layers
14 and 15, respectively.
[0031] As shown, the front radiographic fluorescent screen 21 comprises a support 29, a
reflective layer 27, a fluorescent phosphor layer 25 and a protective layer 23. Similarly,
the back radiographic fluorescent screen 20 comprises a support 28, a reflective
layer 26, a fluorescent phosphor layer 24 and a protective layer 22.
[0032] In practical use, the screen pair and the silver halide element are compressed in
a radiographic cassette with the front screen arranged adjacent and in close contact
with the front silver halide emulsion layer and the back screen is arranged adjacent
and in close contact with the back silver emulsion halide layer. Imagewise X radiation
enters the screen pair and silver halide element combination through the front screen
support 29 and reflective layer 27 and passes the front screen fluorescent phosphor
layer 25. A portion of the X radiation is absorbed in the phosphor layer 25. The remaining
X radiation passes through the protective layers 23 and 17. A small portion of the
X radiation is absorbed in the front silver halide emulsion layer 15, thereby contributing
directly to the formation of a latent image in said front silver halide emulsion layer
15. The major portion of the X radiation passes through the subbing layer 13, the
support 11 and the subbing layer 12. Again, a small portion of the X radiation is
absorbed in the back silver halide emulsion layer 14, thereby contributing directly
to the formation of a latent image in said back silver halide emulsion layer 14. Again,
the major portion of the X radiation passes through the protective layers 16 and
22 and is absorbed in the back fluorescent phosphor layer 24. The imagewise X radiation
is principally absorbed in the fluorescent phosphor layers 24 and 25, thereby producing
the emission of longer wavelength radiation. According to the present invention,
the first radiation emitted by the front fluorescent phosphor layer 25 exposes the
adjacent front silver halide emulsion layer 15, and the second radiation emitted by
the back fluorescent phosphor layer 24 exposes the adjacent back silver halide emulsion
layer 14. The silver halide emulsions are substantially insensitive to the radiation
emitted by the opposite fluorescent phosphor layer. Said radiation emitted by a fluorescent
phosphor layer passing to at least some extent beyond the adjacent silver halide emulsion
layer penetrates the subbing layers and the support to expose the opposite silver
halide emulsion layer. This fact, while increasing to some extent the speed of the
screen pair and silver halide element combination, would have the effect of impairing
the image sharpness by crossover exposure. The terms "actinic" and "non-actinic" radiation
according to the present invention are used to indicate, respectively, radiation of
wavelenght shorter than 500 nm (Ultraviolet and blue radiation), preferably from 300
to less than 500 nm, and radiation of wavelength from 500 nm upwards (green, red and
Infrared radiation), preferably from 500 to 1200 nm. The term "insensitive" as used
herein, describes either primary or intrinsic insensitivity of the silver halide
grain emulsion (or layer including it) to a certain range of wavelengths, as defined,
or secondary or induced insensitivity (or unreachability) of the silver halide emulsion
(or layer including it) in the double silver halide element because of filter action
excercised by a further emulsion layer or layers interposed between the considered
"insensitive" layer and the radiation emitting screen or by filter dyes or agents
included in the considered layer or in such interposed layers. Accordingly, the latent
image formed by radiation (preferably comprised between 300 and 1200 nm) exposure
in each silver halide emulsion layer is primarily formed by exposure to the radiation
emitted by the adjacent fluorescent phosphor layer, with no significant contribution
by opposite screen. Preferably, the radiation exposure necessary to produce a Dmax
of 1.0 on said front silver halide layer will produce a Dmax of less than 0.2 on the
back silver halide emulsion layer under the same development conditions. Conversely,
an exposure at the λ max of the back layer that produces a Dmax of 1.0 will produce
a Dmax of less than 0.2 on the front layer.
[0033] The terms "front" and "back" in the present invention are used to distinguish the
different elements of the unsymmetrical screen pair and double coated silver halide
element combination not their position relating to exposing X radiation source. Accordingly,
X radiation may enter the unsymmetrical screen pair and double-side coated silver
halide element through either the front fluorescent phosphor screen or the back fluorescent
phosphor screen.
[0034] The term "silver halide element" in the present invention includes both silver halide
"photographic" elements which use liquid development to produce the final image and
silver halide "photothermographic" elements, often referred to as "dry silver" elements,
which do not use liquid development to produce the final image, as described thereinafter.
In both photographic and photothermographic silver halide elements, exposure of the
silver halide to radiation produces small clusters of silver ions. The imagewise distribution
of these clusters is known in the art as the latent image. This latent image generally
is not visible by ordinary means and the light-sensitive element must be further processed
in order to produce a visual image. This visual image is produced by the catalytic
reduction of silver which is in catalytic proximity to the specks of the latent image.
The photographic silver halide element is preferably used in medical radiography and
the photothermographic silver halide element is preferably used in industrial radiography.
[0035] Accordingly, the present invention relates to a combination of photosensitive elements
for use in radiography comprising two separate front and back X-ray fluorescent
screens and a silver halide radiographic element comprising a support base and front
and back silver halide emulsion layers each coated on one surface of said support,
wherein said front screen is arranged adjacent to said front silver halide layer and
said back screen is arranged adjacent to said back silver halide layer, and wherein
1) said front screen comprises a first radiation emitting phosphor and said front
silver halide layer comprises silver halide grains sensitive to said first radiation
emitted by said front screen, and
2) said back screen comprises a second radiation emitting phosphor and said back silver
halide layer comprises silver halide grains sensitive to said second radiation emitted
by said back screen, characterized in that
a) said first radiation emitted by said front screen has a wavelength which differs
from said second radiation emitted by said back screen by at least 50 nm,
b) said front silver halide emulsion layer is substantially insensitive to said second
radiation emitted by said back screen, and
c) said back silver halide emulsion layer is substantially insensitive to said first
radiation emitted by said front screen,
the difference in wavelength region of said first and second radiations and the insensitivity
of each silver halide layer to radiation emitted by opposite screen being such to
reduce crossover exposure of at least 10 percent when compared with a symmetrical
combination of a pair of green light emitting fluorescent screens and a double coated
green sensitized silver halide emulsion radiographic element.
[0036] According to a preferred embodiment of this invention, in the combination of a pair
of front and back radiographic fluorescent screens and a double coated silver halide
radiographic element, said front screen comprises a non-actinic radiation, preferably
green light, emitting phosphor and is arranged adjacent to a front silver halide layer
comprising a silver halide emulsion spectrally sensitized to the radiation emitted
by said front screen, and said back screen comprises an actinic radiation, preferably
UV light, emitting phosphor and is arranged adjacent to a back silver halide layer
comprising a silver halide emulsion insensitized to the visually observable regions
of the electromagnetic spectrum (that is 410 to 750 nm).
[0037] Preferably, the phosphors used in the front fluorescent screens applied in the present
invention emit radiation in the green or red region of the visible spectrum. More
preferably, said phosphors emit radiation in the green region of the visible spectrum.
Most preferably, said phosphors emit radiation having more than about 80% of its spectral
emission above 480 nm and its maximum of emission in the wavelength range of 530-570
nm. Green emitting phosphors which may be used in the front fluorescent screens of
the present invention include rare earth activated rare earth oxysulfide phosphors
of at least one rare earth element selected from yttrium, lanthanum, gadolinium and
lutetium, rare earth activated rare earth oxyhalide phosphors of the same rare earth
elements, a phosphor composed of a borate of the above rare earth elements, a phosphor
composed of a phosphate of the above rare earth elements and a phosphor composed of
tantalate of the above rare earth elements. These rare earth green emitting phosphors
have been extensively described in the patent literature, for example in US Patents
4,225,653, 3,418,246, 3,418,247, 3,725,704, 3,617,743, 3,974,389, 3,591,516, 3,607,770,
3,666,676, 3,795,814, 4,405,691, 4,311,487 and 4,387,141. These rare earth phosphors
have a high X-ray stopping power and high efficiency of light emission when excited
with X radiation and enable radiologists to use substantially lower X radiation dosage
levels. Particularly suitable phosphors for use in the front fluorescent screens of
the present invention are terbium or terbium-thulium activated rare earth oxysulfide
phosphors represented by the general formula (I)
(Ln
1-a-b, Tb
a, Tm
b)2 O₂S (I)
wherein Ln is at least one rare earth element selected from lanthanum, gadolinium
and lutetium, and a and b are numbers such as to meet the conditions 0.0005 ≦ a ≦
0.09 and 0 ≦ b ≦ 0.01, respectively, and terbium or terbium-thulium activated rare
earth oxysulfide phosphors represented by the general formula (II)
(Y
1-c-a-b, Ln
c, Tb
a, Tm
b)₂O₂S (II)
wherein Ln is at least one rare earth element selected from lanthanum, gadolinium
and lutetium, and a, b and c are numbers such as to meet the conditions 0.0005 ≦ a
≦ 0.09, 0 ≦ b ≦ 0.01 and 0.65 ≦ c ≦ 0.95, respectively.
[0038] Figure 2 shows an emission spectrum of a front fluorescent screen comprising a fluorescent
layer of (Gd₁₋₀.₀₅, Tb₀.₀₅)₂O₂S phosphor as green emitting phosphor, expressed as
fluorescence (F) versus wavelengths (nm).
[0039] The front silver halide emulsion layer, to be arranged according to this invention
adjacent to the front fluorescent screen, comprises silver halide grains which are
optically sensitized to the spectral region of the radiation emitted by the screens,
preferably to a spectral region of an interval comprised within 25 nm from the wavelength
of the maximum emission of the screen, more preferably within 15 nm, and most preferably
within 10 nm. The silver halide grains of the front silver halide layer have adsorbed
on their surface spectral sensitizing dyes that exhibit absorption maxima in the
regions of the visible spectrum where the front fluorescent screen emits. Preferably,spectral
sensitizing dyes according to this invention are those which exhibit J aggregates
if adsorbed on the surface of the silver halide grains and a sharp absorption band
(J-band) with a bathocromic shifting with respect to the absorption maximum of the
free dye in aqueous solution. Spectral sensitizing dyes producing J aggregates are
well known in the art, as illustrated by F. M. Hamer, Cyanine Dyes and Related Compounds,
John Wiley and Sons, 1964, Chapter XVII and by T. H. James, The Theory of the Photographic
Process, 4th edition, Macmillan, 1977, Chapter 8.
[0040] In a preferred form, J-band exhibiting dyes are cyanine dyes. Such dyes comprise
two basic heterocyclic nuclei joined by a linkage of methine groups. The heterocyclic
nuclei preferably include fused benzene rings to enhance J aggregation.
[0041] The heterocyclic nuclei are preferably quinolinium, benzoxazolium, benzothiazolium,
benzoselenazolium, benzimidazolium, naphthoxazolium, naphthothiazolium and naphthoselenazolium
quaternary salts.
[0042] J-band type dyes preferably used in the present invention have the following general
formula (III):

wherein
Z₁ and Z₂ may be the same or different and each represents the elements necessary
to complete a cyclic nucleus derived from basic heterocyclic nitrogen compounds such
as oxazoline, oxazole, benzoxazole, the naphthoxazoles (e.g., naphth{2,1-d}oxazole,
naphth{2,3-d}oxazole, and naphth{1,2-d}oxazole), thiazoline, thiazole, benzothiazole,
the naphthothiazoles (e.g., naphtho{2,1-d}thiazole), the thiazoloquinolines (e.g.,
thiazolo{4,5-b}quinoline), selenazoline, selenazole, benzoselenazole, the naphthoselenazoles
(e.g., naphtho{1,2-d}selenazole, 3H-indole (e.g., 3,3-dimethyl3H-indole), the benzindoles
(e.g., 1,1-dimethylbenzindole), imidazoline, imidazole, benzimidazole, the naphthimidazoles
(e.g., naphth{2,3-d}imidazole), pyridine, and quinoline, which nuclei may be substituetd
on the ring by one or more of a wide variety of substituents such as hydroxy, the
halogens (e.g., fluoro, bromo, chloro, and iodo), alkyl groups or substituted alkyl
groups (e.g., methyl, ethyl, propyl, isopropyl, butyl, octyl, dodecyl, 2-hydroxyethyl,
3-sulfopropyl, carboxymethyl, 2-cyanoethyl, and trifluoromethyl), aryl groups or substituted
aryl groups (e.g., phenyl, 1-naphthyl, 2-naphthyl, 4-sulfophenyl, 3-carboxyphenyl,
and 4-biphenyl), aralkyl groups (e.g., benzyl and phenethyl), alkoxy groups (e.g.,
methoxy, ethoxy, and isopropoxy), aryloxy groups (e.g., phenoxy and 1-naphthoxy),
alkylthio groups (e.g., ethylthio and methylthio), arylthio groups (e.g., phenylthio,
p-tolythio, and 2-naphthylthio), methylenedioxy, cyano, 2-thienyl, styryl, amino or
substituted amino groups (e.g., anilino, dimethylanilino, diethylanilino, and morpholino),
acyl groups (e.g., acetyl and benzoyl), and sulfo groups,
[0043] R₁ and R₂ can be the same or different and represent alkyl groups, aryl groups, alkenyl
groups, or aralkyl groups, with or without substituents, (e.g., carboxymethyl, 2-hydroxyethyl,
3-sulfopropyl, 3-sulfobutyl, 4-sulfobutyl, 2-methoxyethyl, 2-sulfatoethyl, 3-thiosulfatoethyl,
2-phosphonoethyl, chlorophenyl, and bromophenyl), R₃ represents a hydrogen atom,
R₄ and R₅ can be the same or different and represent a hydrogen atom or a lower alkyl
group of from 1 to 4 carbon atoms,
p and q are 0 or 1, except that both p and q preferably are not 1,
m is 0 or 1 except that when m is 1 both p and q are 0 and at least one of Z₁ and
Z₂ represents imidazoline, oxazoline, thiazoline, or selenazoline,
A is an anionic group,
B is a cationic group, and
k and 1 may be 0 or 1, depending on whether ionic substituents are present. Variants
are, of course, possible in which R₁ and R₃, R₂ and R₅, or R₁ and R₂ together represent
the atoms necessary to complete an alkylene bridge.
[0044] In the most preferred form of this invention, wherein the phosphors of the front
fluorescent screen are rare earth phosphors emitting in the green region of the visible
spectrum, said optical sensitizing dyes adsorbed on said silver halide grains of the
front silver halide layer are represented by the following general formula (IV):

wherein
R₁₀ represents a hydrogen atom or a lower alkyl group of from 1 to 4 carbon atoms
(e.g. methyl, and ethyl),
R₆, R₇, R₈ and R₉ each represents a hydrogen atom, a halogen atom (e.g. chloro, bromo,
iodo, and fluoro), a hydroxy group, an alkoxy group (e.g. methoxy and ethoxy), an
amino group (e.g. amino, methylamino, and dimethylamino), an acylamino group (e.g.
acetamido and propionamido), an acyloxy group (e.g. acetoxy group), an alkoxycarbonyl
group (e.g. methoxycarbonyl, ethoxycarbonyl, and butoxycarbonyl), an alkyl group (e.g.
methyl, ethyl, and isopropyl), an alkoxycarbonylamino group (e.g. ethoxycarbonylamino)
or an aryl group (e.g. phenyl and tolyl), or, together, R₆ and R₇ and, respectively,
R₈ and R₉ can be the atoms necessary to complete a benzene ring (so that the heterocyclic
nucleus results to be, for example, an α-naphthoxazole nucleus, a β-naphthoxazole
or a β,β′-naphthoxazole),
R₁₁ and R₁₂ each represents an alkyl group (e.g. methyl, propyl, and butyl), a hydroxyalkyl
group (e.g. 2-hydroxyethyl, 3-hydroxypropyl, and 4-hydroxybutyl), an acetoxyalkyl
group (e.g. 2-acetoxyethyl and 4-acetoxybutyl), an alkoxyalkyl group (e.g. 2-methoxyethyl
and 3-methoxypropyl), a carboxyl group containing alkyl group (e.g. carboxymethyl,
2-carboxyethyl, 4-carboxybutyl, and 2-(2-carboxyethoxy)-ethyl), a sulfo group containing
alkyl group (e.g. 2-sulfoethyl, 3-sulfopropyl, 4- sulfobutyl, 2-hydroxy3- sulfopropyl,
2-(3-sulfopropoxy)-propyl, p-sulfobenzyl, and p-sulfophenethyl), a benzyl group, a
phenetyl group, a vinylmethyl group, and the like,
X⁻ represents an acid anion (e.g. a chloride, bromide, iodide, thiocyanate, methylsulfate,
ethylsulfate, perchlorate, and p-toluensulfonate ion), and
n represents 1 or 2.
[0045] The alkyl groups included in said substituents R₆, R₇, R₈, R₉, R₁₀, and R₁₁ and,
more particularly, the alkyl portions of said alkoxy, alkoxycarbonyl, alkoxycarbonylamino,
hydroxyalkyl, acetoxyalkyl groups and of the alkyl groups associated with a carboxy
or sulfo group each preferably contain from 1 to 12, more preferably from 1 to 4 carbon
atoms, the total number of carbon atoms included in said groups preferably being
no more than 20.
[0046] The aryl groups included in said substituents R₆, R₇, R₈ and R₉ each preferably contain
from 6 to 18, more preferably from 6 to 10 carbon atoms, the total number of carbon
atoms included in said groups arriving up to 20 carbon atoms.
[0047] The following are specific examples of J-band sensitizing dyes belonging to those
represented by the general formula (IV) above:

[0048] Figure 3 shows the sensitivity spectrum of a front silver halide layer comprising
silver bromoiodide grains comprising 2.3 mole percent iodide and having adsorbed on
their surface the optical sensitizing dye A above, expressed as sensitivity (S) versus
wavelengths (nm).
[0049] Preferably, the phosphors used in the back fluorescent screens applied in the present
invention emit radiation in the ultraviolet region of the electromagnetic spectrum.
More preferably, said phosphors emit radiation having more than about 80% of their
spectral emission below 410 nm and their maximum of emission in the wavelength range
of 300-360 nm. Ultraviolet emitting phosphors which may be used in the back fluorescent
screens of the present invention include ultraviolet emitting phosphors known in the
art such as lead or lanthanum activated barium sulfate phosphors, barium fluorohalide
phosphors, lead activated barium silicate phosphors, gadolinium activated yttrium
oxide phosphors, barium fluoride phosphors, alkali metal activated rare earth niobate
or tantalate phosphors etc. Ultraviolet emitting phosphors are described for example
in BE 703,998 and 757,815, in EP 202,875 and by Buchanan et al., J. Applied Physics,
vol. 9, 4342-4347, 1968,and by Clapp and Ginther, J. of the Optical Soc. of America,
vol. 37, 355-362, 1947. Particularly suitable ultraviolet emitting phosphors for use
in the back fluorescent screens of the present invention are those represented by
the general formula (V)
(Y
1-2/3x-1/3y, Sr
x, Li
y) TaO₄
wherein x and y are numbers such as to meet the conditions 10⁻⁵ ≦ x ≦ 1 and 10⁻⁴
≦ y ≦ 0.1as described in EP 202,875.
[0050] Figure 4 shows an emission spectrum of a back fluorescent screen comprising a fluorescent
layer of (Y, Sr, Li)TaO₄ phosphor as ultraviolet emitting phosphor, expressed as
fluorescence (F) versus wavelengths (nm).
[0051] The back silver halide emulsion layer, arranged according to this invention adjacent
to the back actinic light emitting phosphor screen, comprises silver halide grains
which are not optically sensitized but possess the inherent spectral sensitivity of
the known types of photosensitive silver halides. Said inherent spectral sensitivity
of the conventional silver halide emulsions used in photographic films as known ranges
in the ultraviolet and blue region of the electromagnetic spectrum.
[0052] Figure 5 shows the sensitivity spectrum of a back silver halide emulsion layer comprising
silver bromoiodide grains comprising 2.3 percent mole iodide and having no optical
sensitizing dye adsorbed on their surface, expressed as sensitivity (S) versus wavelenghts
(nm).
[0053] According to the present invention, the non-actinic radiation (preferably green light)
emitted by the front screen imagewise exposes the adjacent front silver halide layer
comprising silver halide grains optically sensitized to the radiation emitted by
said screens. Part of said non-actinic radiation reaches the opposite back silver
halide layer but does not crossover expose the silver halide grains of the back silver
halide layer as those grains are not optically sensitized to the radiation emitted
by said front screen. The ultraviolet or blue emission of the back fluorescent screen
undergoes absorption by the adjacent back silver halide layer and imagewise exposes
the silver halide grains which are not optically sensitized, rather than crossover
passing to the opposite front silver halide layer. This is due to the fact that silver
halide grains possess a good inherent absorption of light with a wavelength below
500 nm and a strong light scattering of ultraviolet and blue light through the dispersed
silver halide particles of the emulsion layer. The above implies not having a large
amount of ultraviolet or blue light of the back fluorescent screen to expose the
opposite front silver halide layer. The crossover exposure reduction attained with
the screen pair and double silver halide element combination of this invention is
preferably at least 10 percent, more preferably at least 20 percent in comparison
with a conventional combination of green emitting fluorescent screens and double
coated green sensitized silver halide radiographic element. Accordingly, the image
sharpness is improved by reducing crossover exposure using a unique combination of
conventional silver halide emulsion layers and fluorescent screens.
[0054] The light-sensitive double-side coated silver halide radiographic element comprises
a transparent polymeric base of the type commonly used in radiography, for instance
a polyester base, and in particular a polyethylene terephthalate base.
[0055] In the silver halide photographic elements of this invention, the silver halide emulsions
coated on the two surfaces of the support, the front optically sensitized silver halide
emulsion and the back optically unsensitized silver halide emulsion, may be similar
or different and comprise emulsions commonly used in photographic elements, such
as silver chloride, silver iodide, silver chloro-bromide, silver chloro-bromo-iodide,
silver bromide and silver bromo-iodide, the silver bromoiodide being particularly
useful for radiographic elements. The silver halide grains may have different shapes,
for instance cubic, octahedrical, tabular shapes, and may have epitaxial growths;
they generally have mean sizes ranging from 0.1 to 3 µm, more preferably from 0.4
to 1.5 µm. The emulsion are coated on the support at a total silver coverage comprised
in the range from about 3 to 6 grams per square meter. The silver halide binding material
used is a water-permeable hydrophilic colloid, which preferably is gelatin, but other
hydrophilic colloids, such as gelatin derivatives, albumin, polyvinyl alcohols, alginates,
hydrolized cellulose esters, hydrophilic polyvinyl polymers, dextrans, polyacrylamides,
hydrophilic acrylamide copolymers and alkylacrylates can also be used alone or in
combination with gelatin.
[0056] As regards the processes for silver halide emulsion preparation and use of particular
ingredients in the emulsion and in the light-sensitive element, reference is made
to Research Disclosure 18,431 published in August 1979, wherein the following chapters
are dealt with in deeper details:
IA. Preparation, purification and concentration methods for silver halide emulsions.
IB. Emulsion types.
IC. Crystal chemical sensitization and doping.
II. Stabilizers, antifogging and antifolding agents.
IIA. Stabilizers and/or antifogging.
IIB. Stabilization of emulsions chemically sensitized with gold compounds.
IIC. Stabilization of emulsions containing polyalkylene oxides or plasticizers.
IID. Fog caused by metal contaminants.
IIE. Stabilization of materials comprising agents to increase the covering power.
IIF. Antifoggants for dichroic fog.
IIG. Antifoggants for hardeners and developers comprising hardeners.
IIH. Additions to minimize desensitization due to folding. III. Antifoggants for
emulsions coated on polyester bases.
IIJ. Methods to stabilize emulsions at safety lights.
IIK. Methods to stabilize X-ray materials used for high temperature, Rapid Access,
roller processor transport processing.
III. Compounds and antistatic layers.
IV. Protective layers.
V. Direct positive materials.
VI. Materials for processing at room light.
IX. Spectral sensitization.
X. UV sensitive materials.
XII. Bases.
[0057] The silver halide photothermographic elements of this invention basically comprise
a light insensitive, reducible silver source, a light sensitive material which generates
silver when irradiated, and a reducing agent for the silver source. The light sensitive
material is generally photographic silver halide which must be in catalytic proxymity
to the light insensitive silver source. Catalytic proximity is an intimate physical
association of these two materials so that when silver specks or nuclei are generated
by the irradiation or light exposure of the photographic silver halide, those nuclei
are able to catalyze the reduction of the silver source by the reducing agent. It
has been long understood that silver is a catalyst for the reduction of silver ions
and the silver-generating light sensitive silver halide catalyst progenitor may be
placed into catalytic proximity with the silver source in a number of different fashions,
such as partial metathesis of the silver source with a halogen-containing source (e.g.
US Pat. No. 3,457,075), coprecipitation of the silver halide and silver source material
(e.g. US Pat. No. 3,839,049), and any other method which intimately associates the
silver halide and the silver source.
[0058] The silver source used in this area of technology is a material which contains a
reducible source of silver ions. The earliest and still preferred source comprises
silver salts of long chain fatty carboxylic acids, usually of from 10 to 30 carbon
atoms. The silver salt of behenic acid or mixtures of acids of like molecular weight
have been primarily used. Salts of other organic acids or other organic materials
such as silver imidazolates have been proposed, and British Pat. No. 1,110,046 discloses
the use of complexes of inorganic or organic silver salts as image source materials.
Silver salts of long chain (10 to 30, preferably 15 to 28 carbon atoms) fatty carboxylic
acids are preferred in the practice of the present invention.
[0059] Photothermographic emulsions are usually constructed as one or two layers per side
of the support. Single layer construction must contain the silver source material,
the silver halide, the developer and binder as well as optional additional materials
such as toners, coating aids and other adjuvants. Two-layer constructions must contain
the silver source and the silver halide in an emulsion layer (usually the layer adjacent
the support) and the other ingredients in the second layer or both layers. The silver
source material should constitute from about 20 to 70 percent by weight of the imaging
layer. Preferably it is present as 30 to 55 percent by weight. The second layer in
a two-layer construction would not affect the percentage of the silver source material
desired in the single imaging layer.
[0060] The silver halide may be any photosensitive silver halide as silver bromide, silver
iodide, silver chloride, silver bromoiodide, silver chlorobromoiodide, silver chlorobromide,
etc., and may be added to the emulsion layer in any fashion which places it in catalytic
proximity to the silver source. The silver halide is generally present as 0.75 to
15 percent by weight of the imaging layer, although larger amounts are useful. It
is preferred to use from 1 to 10 percent by weight silver halide in the imaging layer
and most preferred to use from 1.5 to 7.0 percent. The vast list of photographic adjuvants
and processing aids may be used in silver halide emulsion preparation. These materials
include chemical sensitizers (including sulfur and gold compounds), development accelerators
(e.g. onium and polyonium compounds), alkylene oxide polymer accelerators, antifoggant
compounds, stabilizers (e.g. azaindenes, especially the tetra- and pentaazaindenes),
surface active agents (particularly fluorinated surfactants), antistatic agents (particularly
fluorinated compounds), plasticizers, matting agents, and the like.
[0061] The reducing agent for the silver ion may be any material, preferably organic material,
which will reduce silver ion to metallic silver. Conventional photographic developers
such as phenidone, hydroquinones, and cathecol are useful, but hindered phenol reducing
agents are preferred. The reducing agents should be present as 1 to 20 percent by
weight of the imaging layer. In a two-layer construction, if the reducing agent is
in the second layer, slighty higher proportions, of from about 2 to 20 percent tend
to be more desirable.
[0062] Toners such as phthalazinone, phthalazine and phthalic acid are not essential to
the construction, but highly desirable. These materials may be present, for example,
in amounts of from 0.2 to 5 percent by weight.
[0063] The binder may be selected from any of the well known natural and synthetic resins
such as gelatin, polyvinyl acetals, polyvinyl chloride, polyvinyl acetate, cellulose
acetate, polyolefins, polyesters, polystyrene, polyacrylonitrile, polycarbonates,
and the like. Copolymers and terpolymers are, of course, included in these definitions.
The polyvinyl acetals, such as polyvinyl butyral and polyvinyl formal, and vinyl copolymers,
such as polyvinyl acetate/chloride are particularly desirable. The binders are generally
used in a range of 20 to 75 percent by weight of each layer, and preferably about
30 to 55 percent by weight.
[0064] As previously noted, various other adjuvants may be added to the photothermographic
emulsions of the present invention. For example, toners, accelerators, acutance dyes,
sensitizers, stabilizers, surfactants, lubricants, coating aids, antifoggants, leuco
dyes, chelating agents, and various other well known additives may be usefully incorporated.
The use of acutance dyes matched to the spectral emission of the intensifying screen
is particularly desirable.
[0065] The balance in properties of the photothermographic emulsion must be precisely restricted
by the proportions of materials in the emulsion. The proportions of the silver salt
and organic acid are particularly critical in obtaining necessary sensitometric properties
in the photothermographic element for radiographic use. In conventional photothermographic
emulsions, it is common to use approximately pure salts of organic acids (e.g., behenic
acid, stearic acid and mixtures of long chain acids) as the substantive component
of the emulsion. Sometimes minor amounts or larger amounts of the acid component
are included in the emulsion. In the practice of the present invention the molar ratio
of organic silver salt to organic acid must be in the range of 1.5/1 to 6.2/1 (salt/acid).
Below that range, the contrast has been found to be too low, and above that range
the speed and background stability of the emulsion drop off unacceptably. It is preferred
that the ratio be in the range of 2.0/1 to 3.50/1.
[0066] The silver halide may be provided by in situ halidization or by use of pre-formed
silver halide.
[0067] The process of industrial radiography would be performed by using a conventional
X-ray projection source or other high energy particle radiation sources including
gamma and neutron sources. As well known in the art, the particular phosphors used
have a high absorption coefficient for the radiation emitted from the source. Usually
this radiation is high energy particle radiation which is defined as any of X-rays,
neutrons and gamma radiation. The industrial material would be placed between the
controllable source of X-rays and the industrial radiographic system of the present
invention. A controlled exposure of X-rays would be directed from the source and through
the industrial material so as to enter and impact the radiographic system at an angle
approximately perpendicular to the plane or surface of the intensifying screens and
the photothermographic film contiguous to the inside surface of the screens. The radiation
absorbed by the phosphors of the screens would cause light to be emitted by the screens
which in turn would generate a latent image in the silver halide grains of the two
emulsion layers. Conventional thermal development would then be used on the exposed
film.
[0068] The X radiation image converting screens of this invention have a fluorescent layer
comprising a binder and a phosphor dispersed therein. The fluorescent layer is formed
by dispersing the phosphor in the binder to prepare a coating dispersion, and then
applying the coating dispersion by a conventional coating method to form a uniform
layer. Although the fluorescent layer itself can be a radiation image converting screen
when the fluorescent layer is self-supporting, the fluorescent layer is generally
provided on a substrate to form a radiation image converting screen. Further, a protective
layer for physically and chemically protecting the fluorescent layer is usually provided
on the surface of the fluorescent layer. Furthermore, a primer layer is sometimes
provided between the fluorescent layer and the substrate to closely bond the fluorescent
layer to the substrate, and a reflective layer is sometimes provided between the substrate
(or the primer) and the fluorescent layer.
[0069] The binder employed in the fluorescent layer of the X radiation image converting
screens of the present invention, can be, for example, one of the binders commonly
used in forming layers: gum arabic, protein such as gelatin, polysaccharides such
as dextran, organic polymer binders such as polyvinylbutyral, polyvinylacetate, nitrocellulose,
ethylcellulose, vinylidene-chloride-vinylchloride copolymer, polymethylmethacrylate,
polybutylmethacrylate, vinylchloride-vinylacetate copolymer, polyurethane, cellulose
acetate butyrate, polyvinyl alcohol, and the like.
[0070] Generally, the binder is used in an amount of 0.01 to 1 part by weight per one part
by weight of the phosphor. However, from the viewpoint of the sensitivity and the
sharpness of the screen obtained, the amount of the binder should preferably be small.
Accordingly, in consideration of both the sensitivity and the sharpness of the screen
and the easiness of application of the coating dispersion, the binder is preferably
used in an amount of 0.03 to 0.2 parts by weight per one part by weight or the phosphor.
The thickness of the fluorescent layer is generally within the range of 10 µm to
1 mm.
[0071] In the radiation image converting screens of the present invention, the fluorescent
layer is generally coated on a substrate. As the substrate, various materials such
as polymer material, glass, wool, cotton, paper, metal, or the like can be used. From
the viewpoint of handling the screen, the substrate should preferably be processed
into a sheet or a roll having flexibility. In this connection, as the substrate is
preferably either a plastic film (such as a cellulose triacetate film, polyester
film, polyethylene terephthalate film, polyamide film, polycarbonate film, or the
like), or ordinary paper or processed paper (such as a photographic paper, baryta
paper, resin-coated paper, pigment-containing paper which contains a pigment such
as titanium dioxide, or the like). The substrate may have a primer layer on one surface
thereof (the surface on which the fluorescent layer is provided) for the purpose of
holding the fluorescent layer tightly. As the material of the primer layer, an ordinary
adhesive can be used. In providing a fluorescent layer on the substrate (or on the
primer layer or on the reflective layer), a coating dispersion comprising the phosphor
dispersed in a binder may be directly applied to the substrate (or to the primer layer
or to the reflective layer).
[0072] Further, in the X radiation image converting screens of the present invention, a
protective layer for physically and chemically protecting the fluorescent layer is
generally provided on the surface of the fluorescent layer intended for exposure
(on the side opposite the substrate). When, as mentioned above, the fluorescent layer
is self-supporting, the protective layer may be provided on both surfaces of the fluorescent
layer. The protective layer may be provided on the fluorescent layer by directly
applying thereto a coating dispersion to form the protective layer thereon, or may
be provided thereon by bonding thereto the protective layer formed beforehand. As
the material of the protective layer, a conventional material for a protective layer
such a nitrocellulose, ethylcellulose, cellulose acetate, polyester, polyethylene
terephthalate, and the like can be used.
[0073] The X radiation image converting screens of the present invention may be colored
with a colorant. Further, the fluorescent layer of the radiation image converting
screen of the present invention may contain a white powder dispersed therein. By using
a colorant or a white powder, a radiation image converting screen which provides an
image of high sharpness can be obtained.
EXAMPLES
[0074] The invention can be better illustrated by reference to the following specific examples
and comparative investigations.
Green Emitting Phosphor Screen GRS₁
[0075] A high resolution green emitting phosphor screen, screen GRS₁, was prepared consisting
of a (Gd₁₋₀.₀₅, Tb₀.₀₅)₂O₂S phosphor with average particle grain size of 3 µm coated
in a hydrophobic polymer binder at a phosphor coverage of 270 g/m² and a thickness
of 70 µm on a polyester support. Between the phosphor layer and the support a reflective
layer of TiO₂ particles in a poly(urethane) binder was coated. The screen was overcoated
with a cellulose triacetate layer.
Green Emitting Phosphor Screen GRS₂
[0076] A medium resolution green emitting phosphor screen, screen GRS₂, was prepared consisting
of a (Gd₁₋₀.₀₅, Tb₀.₀₅)₂O₂S phosphor with average particle grain size of 4 µm coated
in a hydrophobic polymer binder at a phosphor coverage of 480 g/m² and a thickness
of 120 µm on a polyester support. Between the phosphor layer and the support a reflective
layer of TiO₂ particles in a poly(urethane) binder was coated. The screen was overcoated
with a cellulose triacetate layer.
UV Emitting Phosphor Screen UVS₃
[0077] An UV emitting phosphor screen, screen UVS₃, was prepared consisting of the type
NP-3040 (Y, Sr, Li)TaO₄ phosphor of Nichia Kagaku Kogyo K.K. with average particle
grain size of 5.1 µm coated in a hydrophobic polymer binder at a phosphor coverage
of 450 g/m² and a thickness of 110 µm on a polyester support. Between the phosphor
layer and the support a reflective layer of TiO₂ particles in a poly(urethane) binder
was coated. The screen was overcoated with a cellulose triacetate layer.
Light-sensitive Photographic Film GRUVF₁
[0078] A light-sensitive film having a green sensitized silver halide emulsion layer (hereinafter
designated front layer) coated on one side of the support and a spectrally unsensitized
silver halide emulsion layer (hereinafter designated back layer) coated on the other
side of the support, film GRUVF₁, was prepared in the following manner. On one side
of a polyester support was coated a green sensitized silver halide gelatin emulsion
layer containing cubic silver bromoiodide grains (having 2.3 mole percent iodide and
an average grain size of 0.65 µm) at 2.57 g/m² Ag and 1.9 g/m² gelatin. The emulsion
was sulfur and gold chemically sensitized and spectrally sensitized with 1,070 mg/
mole Ag of the green sensitizing Dye A, anhydro-5,5′-dichloro-9-ethyl-3,3′-bis(3-sulfopropyl)-oxacarbocyanine
hydroxyde triethylamine salt. A protective overcoat containing 0.9 g/m² gelatin was
applied to said silver bromoiodide front layer. On the other side of the polyester
support was coated a spectrally unsensitized silver halide silver halide gelatin emulsion
layer containing cubic silver bromoiodide grains (comprising a 1:1 by weight blend
of silver bromoiodide grains having 2 mole percent iodide and an average grain size
of 1.3 µm and silver bromoiodide grains having 2.3 mole percent iodide and an average
grain size of 0.65 µm) at 2.51 g/m² Ag and 1.8 g/m² gelatin. The emulsion was sulfur
and gold chemically sensitized. A protective overcoat containing 0.9 g/m² gelatin
was applied to said silver bromoiodide back layer.
Light-sensitive Photographic Film GRUVF₂
[0079] A light-sensitive film having a green sensitized silver halide emulsion layer (hereinafter
designated front layer) coated on one side of the support and a spectrally unsensitized
silver halide emulsion layer (hereinafter designated back layer) coated on the other
side of the support, film GRUVF₂, was prepared in the following manner. On one side
of a polyester support was coated the green sensitized silver halide gelatin emulsion
layer containing cubic silver bromoiodide grains of the front layer of film GRUVF₁
(having 2.3 mole percent iodide and an average grain size of 0.65 µm) at 2.60 g/m²
Ag and 1.9 g/m² gelatin. The emulsion was sulfur and gold chemically sensitized and
spectrally sensitized with 1,070 mg/Ag mole of the green sensitizing Dye A, anhydro-5,5′-dichloro-9-ethyl-3,3′-bis(3-sulfopropyl)-
oxacarbocyanine hydroxyde triethylamine salt. A protective overcoat containing 0.9
g/m² gelatin was applied to said silver bromoiodide front layer. On the other side
of the polyester support was coated a spectrally unsensitized silver halide silver
halide gelatin emulsion layer containing cubic silver bromoiodide grains of the front
layer of film GRUVF₁ (having 2.3 mole percent iodide and an average grain size of
0.65 µm) at 2.49 g/m² Ag and 1.9 g/m² gelatin. The emulsion was sulfur and gold chemically
sensitized. A protective overcoat containing 0.9 g/m² gelatin was applied to said
silver bromoiodide back layer.
Light-sensitive Photographic Film UVUVF₃
[0080] A light-sensitive film having a spectrally unsensitized silver halide emulsion layer
coated on each side of a support, film UVUVF₃, was prepared in the following manner.
On each side of a polyester support was coated a spectrally unsensitized silver halide
silver halide gelatin emulsion layer containing cubic silver bromoiodide grains of
the front layer of film GRUVF₁ (having 2.3 mole percent iodide and an average grain
size of 0.65 µm) at 2.60 and 2.49 g/m² Ag, respectively, and 1.9 g/m² gelatin. The
emulsion was sulfur and gold chemically sensitized. A protective overcoat containing
0.9 g/m² gelatin was applied to each silver bromoiodide layer.
Light-sensitive Photographic Film GRGRF₄
[0081] A light-sensitive film having a green sensitized silver halide emulsion layer coated
on each side of a support, film GRGRF₄, was prepared in the following manner. On
each side of a polyester support was coated the green sensitized silver halide gelatin
emulsion layer containing cubic silver bromoiodide grains of the front layer of film
GRUVF₁ (having 2.3 mole percent iodide and an average grain size of 0.65 µm) at 2.18
g/m² Ag and 1.9 g/m² gelatin. The emulsion was sulfur and gold chemically sensitized
and spectrally sensitized with 1,070 mg/mole Ag of the green sensitizing Dye A, anhydro-5,5′-dichloro-9-ethyl-3,3′-bis(3-sulfopropyl)-
oxacarbocyanine hydroxyde triethylamine salt. A protective overcoat containing 0.9
g/m² gelatin was applied to each silver bromoiodide layer.
Comparison of Screen Pairs and Light-sensitive Photographic Films
[0082] Pairs of screens in combination with double coated light-sensitive photographic films
described above were exposed as follows. Referring to Figure 1, film-screens combinations
were made in which the front screen was in contact with the front emulsion layer and
the back screen was in contact with the back emulsion layer. Each screen pair-film
combination was exposed to X-rays from a tungsten target tube operated at 80 kVp
and 25 mA from a distance of 120 cm. The X-rays passed through an aluminium step wedge
before reaching the screen-film combination. Following exposure the films were processed
in a 3M Trimatic
TM XP507 processor using 3M XAD/2 developer replenisher and 3M XAF/2 fixer replenisher.
[0083] The speed and the image quality are reported in the following table. Percent crossover
was calculated by using the following equation:

wherein δ logE is the difference in speed between the two emulsion layers of the
same film when exposed with a single screen (the lower the percent crossover, the
better the image quality).
TABLE
Comb. |
Screen Pair Front/Back |
Film |
Rel. Speed log E |
% Crossover |
1 |
GRS₁/GRS₁ |
GRGRF₄ |
0.00 |
37 |
2 |
UVS₃/UVS₃ |
UVUVF₃ |
-0.39 |
9 |
3 |
GRS₁/UVS₃ |
GRUVF₂ |
-0.22 |
4* |
9** |
4 |
GRS₁/UVS₃ |
GRUVF₁ |
0.00 |
9* |
5** |
5 |
GRS₂/UVS₃ |
GRUVF₁ |
+0.18 |
4* |
5** |
* crossover measured in the front emulsion layer |
** crossover measured in the back emulsion layer |
[0084] Sharpness and granularity of the screen pair-film combinations were determined as
follows. Each screen pair-film combination was exposed to X-rays from a tungsten
tube operated at 80 kVp and 25 mA from a distance of 150 cm. The X-rays passed through
a 100 µ thick lead Funk target sold by Huttner Company before reaching the screen-film
combination. Following exposure the films were processed in the 3M Trimatic
TM XP507 processor using 3M XAD/2 developer replenisher and 3M XAF/2 fixer replenisher.
Sharpness and granularity of the processed films were determined by visual examination
of ten observers skilled in making image comparisons. Figures 6 and 7 are graphs illustrating
the sharpness (SH) and granularity (GR) versus the difference of sensitivity δS of
the double coated silver halide element and fluorescent screen pair combinations
and that of green sensitive double coated element combined with green emitting fluorescent
screen pair taken as reference. In the graphs, the higher the numbers of sharpness
and granularity, the better is the sharpness and granularity. Sharpness and granularity
of the UV and blue light sensitive double coated silver halide element combined with
UV emitting fluorescent screen pair are the best but at the lower level of sensitivity,
while sharpness and granularity of the double coated element and screen pair combinations
of this invention are better or comparable to that of green sensitive double coated
element combined with green emitting fluorescent screen pair at comparable or higher
level of sensitivity.
Light-sensitive Photothermographic Film GRBLF₅
a) Preparation of the silver soap.
[0085] To 20 l of water at 80°C were added 634.5 g of Humbo acid 9022 (a long chain fatty
carboxylic acid comprising 90% C₂₀ + C₂₂, 5% C₁₈ and 5% other acid), 131 g Humbo acid
9718 (a long chain fatty carboxylic acid comprising 95% C₁₈ and 5% C₁₆) and 0.44 moles
of a 0.08 µm cubic silver bromoiodide (6% mole iodide) emulsion. While stirring, were
added 89.18 g NaOH dissolved in 1.25 l water, then 19 ml of conc. HNO₃ diluted with
50 ml water. At 55°C were added 364.8 g AgNO₃ dissolved in 2.5 l water at 55°C. The
mixture was heated at 55°C for one hour while stirring slowly, centrifugated while
spray washing until 20,000 ohms resistance of water was obtained and dried.
b) Preparation of the silver salt homogenate.
[0086] Silver soap powder above (12% by weight), toluene (20% by weight) and methylethyl
ketone (68% by weight) were mixed, soaked over-night, added with 12 g polyvinylbutyral
(Butwar
TM B-76) and homogenized at 4,000, then 8,000 PSI.
c) Preparation of the first trip.
[0087] 200 g of the silver soap homogenate above were added with 40 g methylethyl ketone
and 30 g polyvinylbutyral (Butwar
TM B-76) and mixed for one-half hour. The mixture was added with 2.2 ml of a 10% HgBr₂
in methanol, stirred for 5 minutes, then added with 4 g of Nonox
TM W₅₀ Developer of formula

[0088] One 50 g part of the dispersion above was added with 0.6 ml of a solution of 0.04
g per 10 ml of the following blue sensitizer

[0089] A second 50 g part of the dispersion above was added with 0.6 ml of a solution of
0.05 g per 10 ml of the following green sensitizer

d) Coating of the first trip.
[0090] The blue sensitized dispersion above was coated on a clear 4 mil (2 x 10⁻⁴ m) polyethyleneterephthalate
support at 5 mils over the support and dried for 3 minutes at 87°C. On the opposite
side of the support the green sensitized dispersion above was coated at 5 mils over
the support and dried for 3 minutes at 87°C.
e) Preparation of the second trip.
[0091]
|
Component |
Parts by Weight |
A. |
Methylethyl ketone |
78.58 |
B. |
Acetone |
12.02 |
C. |
Methanol |
4.91 |
D. |
FC-431 (3M Fluorocarbon) |
0.04 |
E. |
Phthalazine |
0.59 |
F. |
4-Methyl-phthalic acid |
0.41 |
G. |
Tetrachlorophthalic anhydride |
0.27 |
H. |
Tetrachlorophthalic acid |
0.12 |
I. |
Cellulose acetate ester |
3.06 |
A through H were added to a container and mixed until solids were dissolved. I was
then added and mixed for one hour until was dissolved.
f) Coating of the second trip.
[0092] On the blue sensitizing coating previously applied, the second trip was coated over
the first at 2.25 mils and dried for 3 minutes at 87°C. The film was turned over and,
on the green sensitized coating previously applied, the second trip was coated at
2.25 mils and dried for 3 minutes at 87°C.
g) Evaluation of the film.
[0093] A sample of the finished double-side coated photothermographic film was exposed
with a xenon flash sensitometer through a 460 nanometer narrow band filter at a setting
of 10⁻³ seconds through a 0-4 continous density wedge. The exposed sample was processed
for four seconds at 131°C in a roller driven thermal processor. The sensitometry was
recorded as D
min=0.21 and D
max=4.22. Another sample was exposed and processed as above but using a 560 nanometer
narrow band filter. The sensitometry was recorded as D
min=0.21 and D
max=2.19. Clearly there is no cross-over from the green sensitized layer to the blue
sensitizing layer. The blue sensitized layer when coated singly on one side of a polyester
substrate recorded an image as follows : D
min=0.13 and D
max=2.56.
1. A combination of photosensitive elements for use in radiography comprising two
separate front and back X-ray fluorescent screens and a silver halide radiographic
element comprising a support base and front and back silver halide emulsion layers
each coated on one surface of said support, wherein said front screen is arranged
adjacent to said front silver halide layer and said back screen is arranged adjacent
to said back silver halide layer, and wherein
1) said front screen comprises a first radiation emitting phosphor and said front
silver halide layer comprises silver halide grains sensitive to said first radiation
emitted by said front screen, and
2) said back screen comprises a second radiation emitting phosphor and said back
silver halide layer comprises silver halide grains sensitive to said second radiation
emitted by said back screen,
characterized in that
a) said first radiation emitted by said front screen is in a wavelength region of
non-actinic radiation and said second radiation emitted by said back screen is in
a wavelength region of actinic radiation,
b) said first radiation emitted by said front screen has a wavelength which differs
from said second radiation emitted by said back screen by at least 50 nm,
c) said front silver halide emulsion layer is substantially insensitive to said second
radiation emitted by said back screen, and
d) said back silver halide emulsion layer is sub stantially insensitive to said first
radiation emitted by said front screen,
the difference in wavelength region of said first and second radiations and the insensitivity
of each silver halide layer to radiation emitted by opposite screen being such to
reduce crossover exposure of at least 10 percent when compared with a symmetrical
combination of a pair of green light emitting fluorescent screens and a double coated
green sensitized silver halide radiographic element.
2. The combination of claim 1, wherein
a) said front screen comprises a non-actinic light emitting phosphor and said front
silver halide layer comprises silver halide grains spectrally sensitized to the radiation
emitted by said front screen, and
b) said back screen comprises a UV emitting phosphor and said back silver halide layer
comprises spectrally insensitized silver halide grains.
3. The combination of claim 1, wherein said front screen comprises a substantially
green emitting phosphor.
4. The combination of claim 1, wherein said front screen comprises a green emitting
phosphor having more than 80% of its spectral emission above 480 nm and its maximum
of emission in the wavelength range of 530 - 570 nm.
5. The combination of claim 1, wherein said front screen comprises a green emitting
phosphor represented by the general formula
(Ln1-a-b, Tba, Tmb)₂O₂S
wherein Ln is at least one rare earth selected from lanthanium, gadolinium and lutetium,
and a and b are numbers such as to meet the conditions of 0.0005 ≦ a ≦ 0.09 and 0
≦ b ≦ 0.01, respectively, or the general formula
(Y1-c-a-b,Lnc,Tba,Tmb)₂O₂S
wherein Ln is at least one rare earth selected from lanthanium, gadolinium and lutetium,
and a, b and c are numbers such as to meet the conditions of 0.0005 ≦ a ≦ 0.09, 0
≦ b ≦ 0.01 and 0.65 ≦ c ≦ 0.95, respectively.
6. The combination of claim 1, wherein said front screen comprises a terbium-activated
gadolinium or lanthanium oxysulphide phosphor having substantially emission peaks
at 487 and 545 nm.
7. The combination of claim 1, wherein said front silver halide layer comprises silver
halide grains spectrally sensitized with spectral sensitizing dyes of the cyanine
or merocyanine dyes.
8. The combination of claim 4, wherein said front silver halide layer comprises silver
halide grains spectrally sensitized with sensitizing dyes in such a way that it is
sensitive for light in wavelength range of 530 - 570 nm.
9. The combination of claim 4, wherein said front silver halide emulsion layer comprises
silver halide grains spectrally sensitized with sensitizing dyes represented by the
general formula

wherein R₁₀ represents a hydrogen atom or an alkyl group, R₆, R₇, R₈ and R₉ each
represent a hydrogen atom, a halogen atom, a hydroxy group, an alkoxy group, an amino
group, an acylamino group, an acyloxy group, an alkoxycarbonyl group, an alkyl group,
an alkoxycarbonylamino group or an aryl group, or, together, R₆ and R₇, and respectively
R₈ and R₉ can be the atoms necessary to complete a benzene ring, R₁₁ and R₁₂ each
represent an alkyl group, a hydroxyalkyl group, an acetoxyalkyl group, an alkoxyalkyl
group, a carboxyl group containing alkyl group, a sulfo group containing alkyl group,
a benzyl group, a phenethyl group or a vinylmethyl group, X⁻ represents an acid anion
and n represents 1 or 2.
10. The combination of claim 2, wherein said back screen comprises a UV emitting phosphor
having more than 80% of its spectral emission below 410 nm and its maximum of emission
in the wavelength range of 300 - 360 nm.
11. The combination of claim 2, wherein said back screen comprises a UV emitting phosphor
selected in the class consisting of lead or lanthanum activated barium sulfate phosphors,
barium fluorohalide phosphors, lead activated barium silicate phosphors, gadolinium
activated yttrium oxide phosphors, barium fluoride phosphors, and alkali metal activated
rare earth niobate or tantalate phosphors.
12. The combination of claim 2, wherein said back screen comprises a UV emitting phosphor
corresponding to the general formula
(Y1-2/3x-1/3y, Srx, Liy) TaO₄
wherein x and y are numbers such as to meet the conditions 10⁻⁵ ≦ x ≦ 1 and 10⁻⁴
≦ y ≦ 0.1.
13. The combination of claim 2, wherein said back silver halide layer comprises chemically
sensitized spectrally insensitized silver bromoiodide grains.
14. A method for recording a radiation image comprising the steps of (i) imagewise
exposing to X radiations a combination of photosensitive elements comprising two
separate front and back X-ray fluorescent screens and a silver halide radiographic
element comprising a support base and front and back silver halide emulsion layers
each coated on one surface of said support, wherein said front screen is arranged
adjacent to said front silver halide layer and said back screen is arranged adjacent
to said back silver halide layer, and wherein
1) said front screen comprises a first radiation emitting phosphor and said front
silver halide layer comprises silver halide grains sensitive to said first radiation
emitted by said front screen, and
2) said back screen comprises a second radiation emitting phosphor and said back
silver halide layer comprises silver halide grains sensitive to said second radiation
emitted by said back screen,
and (ii) developing said silver halide radiographic element halide, characterized
in that
a) said first radiation emitted by said front screen has a wavelength which differs
from said second radiation emitted by said back screen by at least 50 nm,
b) said front silver halide emulsion layer is substantially insensitive to said second
radiation emitted by said back screen, and
c) said back silver halide emulsion layer is substantially insensitive to said first
radiation emitted by said front screen,
the difference in wavelength region of said first and second radiations and the insensitivity
of each silver halide layer to radiation emitted by opposite screen being such to
reduce crossover exposure of at least 10 percent when compared with a symmetrical
combination of a pair of green light emitting fluorescent screens and a double coated
green sensitized silver halide radiographic element.
15. The method for recording a radiation image according to claim 14, wherein
a) said front screen comprises a non-actinic radiation emitting phosphor and said
front silver halide layer comprises silver halide grains spectrally sensitized to
the radiation emitted by said front screen, and
b) said back screen comprises a UV emitting phosphor and said back silver halide layer
comprises spectrally insensitized silver halide grains.
16. The method for recording a radiation image according to claim 14, wherein said
front screen comprises a green emitting phosphor having more than 80% of its spectral
emission above 480 nm and its maximum of emission in the wavelength range of 530
- 570 nm.
17. The method for recording a radiation image according to claim 14, wherein said
front screen comprises a green emitting phosphor represented by the general formula
(Ln1-a-b, Tba, Tmb)₂O₂S wherein Ln is at least one rare earth selected from lanthanium, gadolinium
and lutetium, and a and b are numbers such as to meet the conditions of 0.0005 ≦ a
≦ 0.09 and 0 ≦ b ≦ 0.01, respectively, or the general formula
(Y1-c-a-b,Lnc,Tba, Tmb)₂O₂Tb
wherein Ln is at least one rare earth selected from lanthanium, gadolinium and lutetium,
and a, b and c are numbers such as to meet the conditions of 0.0005 ≦ a ≦ 0.09, 0
≦ b ≦ 0.01 and 0.65 ≦ c ≦ 0.95, respectively.
18. The method for recording a radiation image according to claim 14, wherein said
front screen comprises a terbium-activated gadolinium or lanthanium oxysulphide
phosphor having substantially emission peaks at 487 and 545 nm.
19. The method for recording a radiation image according to claim 14, wherein said
front silver halide layer comprises silver halide grains spectrally sensitized with
spectral sensitizing dyes of the cyanine or merocyanine dyes.
20. The method for recording a radiation image according to claim 14, wherein said
front silver halide layer comprises silver halide grains spectrally sensitized with
sensitizing dyes in such a way that it is sensitive for light in wavelength range
of 530 - 570 nm.
21. The method for recording a radiation image according to claim 14, wherein said
front silver halide emulsion layer comprises silver halide grains spectrally sensitized
with sensitizing dyes represented by the general formula

wherein R₁₀ represents a hydrogen atom or an alkyl group, R₆, R₇, R₈ and R₉ each
represent a hydrogen atom, a halogen atom, a hydroxy group, an alkoxy group, an amino
group, an acylamino group, an acyloxy group, an alkoxycarbonyl group, an alkyl group,
an alkoxycarbonylamino group or an aryl group, or, together, R₆ and R₇, and respectively
R₈ and R₉ can be the atoms necessary to complete a benzene ring, R₁₁ and R₁₂ each
represent an alkyl group, a hydroxyalkyl group, an acetoxyalkyl group, an alkoxyalkyl
group, a carboxyl group containing alkyl group, a sulfo group containing alkyl group,
a benzyl group, a phenethyl group or a vinylmethyl group, X⁻ represents an acid anion
and n represents 1 or 2.
22. The method for recording a radiation image according to claim 14, wherein said
back screen comprises a UV emitting phosphor having more than 80% of its spectral
emission below 410 nm and its maximum of emission in the wavelength range of 300 -
360 nm.
23. The method for recording a radiation image according to claim 14, wherein said
back screen comprises a UV emitting phosphor selected in the class consisting of lead
or lanthanum activated barium sulfate phosphors, barium fluorohalide phosphors, lead
activated barium silicate phosphors, gadolinium activated yttrium oxide phosphors,
barium fluoride phosphors, and alkali metal activated rare earth niobate or tantalate
phosphors.
24. The method for recording a radiation image according to claim 14, wherein said
back screen comprises a UV emitting phosphor corresponding to the general formula
(Y1-2/3x-1/3y, Sry, Liz) TaO₄
wherein x and y are numbers such as to meet the conditions 10⁻⁵ ≦ x ≦ 1 and 10⁻⁴
≦ y ≦ 0.1.
25. The method for recording a radiation image according to claim 14, wherein said
back silver halide layer comprises chemically sensitized spectrally insensitized
silver bromoiodide grains.
26. A silver halide radiographic element comprising a support base and front and
back silver halide emulsion layers each coated on one surface of said support, characterized
in that said front silver halide emulsion layer comprises silver halide grains sensitive
to a wavelength region of the non-actinic radiation, and said back silver halide
emulsion layer comprises UV or blue sensitive silver halide grains.
27. A combination of photosensitive elements for use in radiography comprising two
separate front and back X-ray fluorescent screens and a silver halide radiographic
element comprising a support base and front and back silver halide emulsion layers
each coated on one surface of said support, wherein said front screen is arranged
adjacent to said front silver halide layer and said back screen is arranged adjacent
to said back silver halide layer, and wherein
1) said front screen comprises a first radiation emitting phosphor and said front
silver halide layer comprises silver halide grains sensitive to said first radiation
emitted by said front screen, and
2) said back screen comprises a second radiation emitting phosphor and said back
silver halide layer comprises silver halide grains sensitive to said second radiation
emitted by said back screen,
characterized in that
a) said first radiation emitted by said front screen has a wavelength which differs
from said second radiation emitted by said back screen by at least 50 nm,
b) said front silver halide emulsion layer is substantially insensitive to said second
radiation emitted by said back screen, and
c) said back silver halide emulsion layer is substantially insensitive to said first
radiation emitted by said front screen,
the difference in wavelength region of said first and second radiations and the insensitivity
of each silver halide layer to radiation emitted by opposite screen being such to
reduce crossover exposure of at least 10 percent when compared with a symmetrical
combination of a pair of green light emitting fluorescent screens and a double coated
green sensitized silver halide radiographic element.
28. A combination of photosensitive elements for use in radiography comprising two
separate front and back X-ray fluorescent screens and a silver halide radiographic
element comprising a support base and front and back silver halide emulsion layers
each coated on one surface of said support, wherein said front screen is arranged
adjacent to said front silver halide layer and said back screen is arranged adjacent
to said back silver halide layer, and wherein
1) said front screen comprises a first radiation emitting phosphor and said front
silver halide layer comprises silver halide grains sensitive to said first radiation
emitted by said front screen, and
2) said back screen comprises a second radiation emitting phosphor and said back
silver halide layer comprises silver halide grains sensitive to said second radiation
emitted by said back screen,
characterized in that
a) said first radiation emitted by said front screen is in a first wavelength region
of the electromagnetic spectrum and said second radiation emitted by said back screen
is in a second wavelength region of the electromagnetic spectrum,
b) said front silver halide emulsion layer is substantially insensitive to said second
radiation emitted by said back screen, and
c) said back silver halide emulsion layer is substantially insensitive to said first
radiation emitted by said front screen.