PHOSPHOR-CONTAINING COMPOSITIONS AND THEIR USE IN X-RAY PHOTOGRAPHY

EMPLOI EN PHOTORADIOGRAPHIE DE SUBSTANCES CONTENANT DES PRODUITS PHOSPHORESCENTS

English Abstract

-1-
Abstract of the Disclosure
Phosphor-containing compositions and their use in X-ray
photography.
A composition of matter is described suitable for
use as fluorescent screen in X-ray photography. The com-
position of matter comprises halide-containing phosphor
particles and in order to improve the stability against
moisture of these particles, a non-metal organic com-
pound of the formula
R-X or X-R'-X
wherein R and R1 are organic groups preferably comprising
at least 6 C-atoms, and not containing a reactive hydro-
gen as does X, and
X is a group containing a reactive hydrogen atom. The
compound has a solubility of not more than 5 g in 100 ml
of water at 15°C.
GV.996

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A composition of matter including halide-containing
phosphor particles, which are halide-containing rare-earth
metal compounds in which one rare-earth metal is present as
a host metal and at least one rare-earth metal is present as
an activator metal, in contact with or reacted with at least
one non-metal organic compound corresponding to one of the
following general formulae:
R-X and X-R -X
wherein:
R represents a monovalent organic group,.
R1 represents a bivalent organic group, with the proviso that
these R and R1 groups contain no reactive hydrogen such
as contained in X, and
X represents a group containing reactive hydrogen, said
compound upon reacting with acetyl chloride being capable
of splitting off chlorine in the form of hydrogen chloride
in the circumstances of the test A wherein stoichiometric
amounts of acetyl chloride and of the organic compound to
be examined are dissolved in anhydrous benzene and re-
fluxed therein for 24 hours in the presence of a stoichio-
metric amount of pyridine; the pyridinium chloride formed
being separated from the cooled reactive mixture at 20°C.
by filtering or centrifuging; if pyridinium chloride
crystals are contained in the cooled reaction mixture, the
compound is usable as a stabilizing agent herein, said com-
pound having a solubility at 15°C. of no more than 5 g in
22

100 ml of water, said compound being present in an amount
sufficient to protect the fluorescence power of said phos-
phor particles from moisture.
2. A composition according to claim 1, wherein the phos-
phor particles bearing one or more of said organic substances
affording protection against moisture are dispersed in a binder.
3. A composition of matter according to claim 1, which
composition includes halide-containing phosphor particles by
admixture combined with at least one said organic substance,
wherein said substance when used in the circumstances of the
following test is capable of maintaining the fluorescent light-
emitting power of the test-phosphor to a level of at least 25%
of its original fluorescent light-emitting power, said test
comprising the following steps:
(1) the production of X-ray image intensifying screens (A) and
(B),
(2) a moisture treatment of screen (A),
(3) an X-ray exposure of said screens (A) and (B) in contact
with distinct areas of a photographic silver halide emulsion
material and the development of said material,
(4) the measurement of the spectral densities obtained in the
areas of said material that have been exposed in contact with
said screens (A) and (B), and
(5) the computation of the actual loss of fluorescent light-
emitting power of the moisture-treated screen (A) in comparison
with screen (B) from the spectral density results obtained in
step (4),
23

- the production of the X-ray image intensifying screen (A)
proceeding as follows:
100 g of terbium-activated lanthanum oxybromide phosphor, 0.5 g
of the substance to be tested,
12.5 g of poly(vinyl-n-butyral) containing still 12% by weight
of non-acetalized vinyl alcohol units and having an average
molecular weight of 50,000 and 48 g of ethylene glycol mono-
methyl ether are ball-milled to a fineness of grind corresponding
with 7 NS Hegman measured with the Hegman gauge as specified in
ASTM D1210, whereupon the dispersion obtained is filtered and
after deaeration coated onto a baryta-coated paper of 290 g per
sq.m at a coverage of 500 g per sq.m to form said X-ray image
intensifying screen A,
- the production of the X-ray image intensifying screen (B)
proceeding as described for screen (A) with the difference that
the substance to be tested is left out of the composition of the
screen,
- the moisture treatment of screen (A) proceeding by covering
congruently the phosphor coating of screen (A) with a wet cir-
cular piece of filter paper having a weight of 1.355 g in dry
state, a diameter of 15 cm and a water-content of 3.100 g,
thereupon air-tight packing the thus covered screen (A) in a
polyethylene bag and keeping the thus packed covered screen (A)
at 60°C for 64 h in a ventilated cabinet followed by the re-
moving of said screen (A) from the bag and after removal of the
filter paper drying at the air at 80°C for 30 min,
- X-ray exposure of the thus treated screen (A) and untreated
screen (B) proceeding while having said screens with the phosphor
24

coating in contact with the silver halide emulsion layer side
of a same photographic silver halide emulsion material with
transparent base, the X-ray exposure and the subsequent devel-
opment of the silver halide material being such that with screen
(B) a spectral density of at least 1.00 above inherent fog is
obtained in the silver halide material area contacting screen
(B); the silver halide material and development are such that
after gradually increasing exposures with screen (B) a silver
image is obtained whose density versus log exposure curve has
a gamma value of 3;
- the measurement of the transmission spectral densities DA and
DB proceeding in the areas of the developed silver halide emul-
sion material that during the exposure have been in contact with
screens (A) and (B) respectively;
- the computing of the actual loss of fluorescent light-emitting
power of the moisture treated screen (A) in comparison with
screen (B) proceeding on the basis of the spectral density re-
sults DA and DB and the gamma 3.
4. A composition of matter in the form of an X-ray image
fluorescent screen, which comprises said composition of claim 1
in a layer containing a binding agent.
5. A composition of matter according to any of claims 1,
2 and 3, wherein said organic compound is an organic compound
wherein the reactive hydrogen atom is linked directly to a sul-
phur atom, or which compound contains the reactive hydrogen atom
in an amino group, a carboxyl group or a hydroxyl group.

6. A composition according to claim 4, wherein the host metal is
yttrium, gadolinium, lanthanum or cerium and the activator metal is
at least one of the metals of the group of terbium, europium,
dysprosium, thulium, samarium and ytterbium.
7. A composition according to claim 4, wherein the rare-earth
metal compound corresponds to one of the following formulae :
<IMG>
wherein X is halogen and n is from 0.006 to 0.0001,
or
<IMG>
wherein X is chlorine or bromine
w is 0.0005 to 0.006 mole of the oxyhalide, and
y is 0.00005 to 0.005 per mole of the oxyhalide.
8. A composition according to claim 4, wherein said rare-earth
metal compound is a terbium-activated lanthanum oxybromide phosphor.
9. A composition according to any of claims 1, 2 and 3, wherein
the phosphor particles and the organic compound are present in a
binding agent consisting of a halogen-free polymer or copolymer.
GV 996 26

Description

~L639~
Phosphor-containi~g compositions and their use in X-ray
~hoto~ra~hv
~ he present invention relates to phosphor-containing
compositions of matter and more particularly to improved
radiation conversion screens comprising halide contain-
ing phosphors and a process for produclng such composi-
tions and screens.
A first class of radiation conversion screens are
X-ray intensifying screens containing fluorescent sub-
stances which are employed for absorbing X-rays and con-
verting sald rays into Iight to which silver halide of a
photographic material is more sensitive than to direct
X-ray exposure. ~hese screens also called radiographic
intensifying screens are customarily arranged inside a
cassette, so that each side of a silver halide film~
emulsion-coated on bo-th sides, after~the cassette has
been closed is in ~ntimate contact with an adjacent screen.
In exposing the film the X-rays pass through one side of
the cassette, through one entire intensifying (front)
screen, through the light-sensitive silver halide film
emulsion-coated on both sides and strike the fluorescent
substances (phosphor particles) of the second (rear) in-
tensifying screen. This causes both screens -to ~luoresce
and to emit fluorescent light into at least the adjacent
silver halide emulsion la~er, which is inherently sensi-
GV.9g6
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'
-, :
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tive or spectrally sensiti~ed to the light emitted by
the screens~
A second class of radiation conversion screens are
the so-called "fluoroscopic screens". Such screens have
the function of producing a direc-tly viewable image in
correspondence with a pattern of penetrating radiation~
A third class of radiation conversion screens are
fluorescent screens used in conjunction with a photo-
cathode that emits photoelectrons under the influence of
the fluorescent light of the screen. Such screens find
application e.g. in image intensifier or image conversion
tubes. In said tubes normally also a fluorescent screen
is present which transforms the impact of fast moving
electrons in light.
~he commonly used ~-ray intensifying screens co~prise
a support and a layer of fluorescent particles dispersed
in a coherent film-forming macromolecular binder medium~
Normally a protective coating is applied on top of the
fluorescent layer to shield said layer from ambient in-
fluences e.g. moisture, air and mechanical abrasion.
Usually these protective coatings are composed of
cellulose derivatives or synthe-tic polymers as described,
e.g., in the United States Patent Specification 3,164,719
of Herbert Bauer, issued January 5, 1965.
Generally, layers comprising cellulosic derivatives
are somewhat permeable to moisture and therefore more
hydrophobic but also more costly synthetic polymers e.g.
polymers containing fluorine atoms are applied to shield
the phosphor layer from moisture.
~he protection from moisture is required not only to
prevent the fluorescent layer from staining but also to
prevent water from adsorbing to the phosphor particles.
Unlike calcium tungstate a broad class of halide co~tain-
ing phosphors is more or less hygroscopic and even small
G~.9g6

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amounts of water reduce the fluorescent light-emitting power
of the phospor after a certain time so that the intensifying
screen becomes useless in the long run.
So far one has only tried to remedy these defects as
described in the United States Patent Specifications 3,164,719,
already mentioned hereinbefore and 3,836,784 of Clayton W. Bates
and Reichard A. Wallace, issued September 17, 1974, e.g. by
mixing the phosphor particles with a hydrophobic polymeric binder
or by coating the phosphor layer with a special protective h-ighly
water-impermeable layer. The hydrophobic polymers have to be
used in rather large amounts, which reduces the light-emitting
power of the screen.
The protective layers do not always have the desired mech-
anical strength and adherence to the phosphor layer and often
require a high temperature coating procedure because of poor
solubility of the polymers.
It is an object of the present invention to provide a
composition of matter, which incorporates halide-containing
phosphor particles, and wherein the phosphor particles are better
protected against the influence of moisture and loss of fluore-
scence power.
It is more particularly an object of the present invention
to provide better moisture-resistant radiation conversion screens
incorporating particles of a halide-containing phosphor.
It is another object of the present invention to provide
~a process for preparing such screens having an improved stability
with respect to their fluorescent light-emitting power.
In accordance with the present invention a composition of
~'

of matter is provided, which composition includes halide-con-
taining phosphor particles, and ~hich are halide-con-taining rare-
earth metal compounds in whihc one rare-earth metal is present
as a host metal and at least one rare-earth metal is present as
an activator metal, and which are admixed or combined in contact
with or have reacted with at least one organic compound in such
a way that the Eluorescing power oE the phosphor particles is
less susceptible to the deleterious influence of humidity and
wherein said organic compound is a non-metal organic compound
corresponding to one of the following general formulae:
R-X and X-R -X
wherein:
R represents a monovalent organic group, preferably of at
least 6 carbon atoms e.g. a hydrocarbon group,
R represents a bivalent oryanic group, preferably of at
least 6 carbon a~oms, e.g. a bivalent hydrocarbon group,
with the proviso that these R and Rl groups contain no
reactive hydrogen such as contained in X, and
X represents a group containing reactive hydrogen, said
compound upon reacting with acétyl chloride being capable
of splitting off chlorine in the form of hydrogen chloride
in the circumstances of the test A wherein stoichiometric
amounts of acetyl chloride and of the organic compound to
be examined are dissolved in anhydrous benzene and refluxed
therein for 24 hours in the presence of a stoichiometric
amount of pyridinei the pyridinium chloride formed being
separated from the cooled reactive mixture at 20C. by
filtering or centrifuging; if pyridinium chloride crystals

are contained in the cooled reaction mixture, the compound
is usable as a ~tabilizing agent herein, said compound
having a solubility at 15C. of no more than 5 g in 100 ml
of water, said compound being present in an amount suffi-
cient to protect the fluoresence power of said phosphor
particles from moisture.
In the formula X-Rl-X the groups X may be the same or
different chemical groups.
Test A
Stoichiometric amounts of acetyl chloride and of the or-
ganic compound to be examined are dissolved in anhydrous benzene
and refluxed herein for 24 h in the presence of a stoichiometric
amount of pyridine. The pyridinium chloride formed is separated
from the cooled reactive mixture (20C) by filtering or centri-
fuging. If pyridinium chloride crystals happen to be contained
in the cooled reaction mixture, the compound meets the demand,
viz. to be usable as a stabilising agent in the present invention.
. . ~
.
~, .. .
- 4a -
. ~ .

~ 3
-- 5 --
If the organic compolmd to be examined is a primary
or secondary amine, pyridine may be omit-ted from the
reac-tion mixture and the chlorides corresponding with
these amines form in -the reaction.
Pyridine is normally used as hydrogen chloride sca-
venger in alcoholysis (see John H.Bil]man and Elisabeth
S.Cleland in Methods of Synthesis in Organic ~hemistry -
Edward Brothers, Inc. Ann ~rbor, Mich., U.S.A. (1951) 78.
The use of pyridine as condensing agent in the prepara-
tion of acid anhydrides star-ting from a carboxylic acid
chloride and a carboxylic acid has been described by
Wagner and Zook, Synthetic Organic Chemistry - John Wiley
and Sons (1953) 558~ -
Suitable non-metal organic compounds are non-rnetal
organic compounds according to the above general formulae
wherein X is a mercapto group9 a primary or secondary
amino group, a carboxyl group or a hydroxyl group, which
is linked to an aliphatic group or aromatic nucleus.
l'he invention includes compositions of matter as
hereinbefore defined wherein (an) organic compound(s)
having said effect of stabilising the phosphor against
the influence of moisture (is) are present at the surfaces
of the phosphor particles. Such compound(s) is (are)
applied to or deposited on the phosphor particles, or
result from a reaction with such phosphor particles e.g
after it (-they) has (have) been dissolved in a liquid
medium and then brought in dissolved state into contact
with the phosphor particles.
lhe invention includes compositions of matter as
hereinbefore defined wherein the phosphor particles bearing
one or more organic compounds affording protection against
moisture are dispersed in a binder.
~ he invention also includes any intensifying screen
consisting of or incorporating a layer formed wholly or in
GV.996

-- 6 --
part of a composition of matter according to the inven-
tion as above defined, with or without any one or more
of the optional features above or hereinafter referred to.
A preferred optional feature resides in the employ-
ment as agent for the purposes of reducing the adverseeffects of moisture on the phosphor, of an organic com-
pound or a combination of such compounds whose potential
protective power satisfies a certain test. ~his test
(hereafter called -the "Standard ~est") has been devised
for the purpose of assessing the level of effectiveness
of any selected organic compounds for phosphor protection
in accordance with the invention and is as follows :
Standard test
_ _ _ _ _ _
(1) An X-ray image in-tensifying screen (~creen A) is pre-
pared from the following composition :
terbium-activated lanthanum oxybromide
phosphor 100 g
organic substance (compound or combination
of organic compounds) -to be tested 0.5 g
poly~vinyl-n-butyral) containing 12%
by weight of non-acetalized vinyl alcohol
units and having an average molecular
weight of 50,000 12~5 g
ethylene glycol monomethyl ether 4~ g
by ball-milling to reduce the particle size to 7
Hegman ~ineness measured with a ~egman gage as
specified in AS~ 1210, fil-tering the resulti~g
dispersion, de-aerating it and applying the com-
position to a baryta-coated paper of 290 g per m2
at a coverage of 500 g/m2.
(2) A second X-ray image i~tensifying screen (screen B)
is prepared in the same way as screen A except that
the organic substance to be tested is omitted.
(3) Screen A is treated with moisture by applying onto the
phosphor layer of the screen a wet circular piece of
filter paper having a dry weight of 1.355 g, a dia-
GV.996

meter of 15 c~ and a water content of 3100 g, air-
tightly enclosing the screen A together with the
applied filter paper in a polyethylene bag, keeping the
bag for 64 h at 60C in a ventilated cabinet and then
removing the screen from the bag, removing the filter
paper and drying the screen in air for 30 min at 80C.
(4) ~he screens A and B (the former having been moisture-
treated as above described) are subjected to an X-ray
exposure while the phosphor layers are in contact with
distinct areas of the same silver halide emulsion
layer of a photographic material having a transparent
emulsion layer support and the e~posed photographic
material is developed~ the X-ray exposure and develop-
ment being such that in the area of the emulsion layer
which was in contact with screen B a spectral density
of at least 1.00 above inherent fog is obtained; and
the composition of the silver halide material and
the development being such that gradually increasing
exposures of the silver halide emulsion area in contact
with screen ~ would give a silver image density versus
log exposure curve having a gamma value (maximum gra-
dient of the characteri~stic curve) of 3;
(5) the densities DA and DB obtained in the areas of the
emulsion layer, which were exposed in contact with
screens A and B are measured;
(6) the actual loss of fluorescent light-emitting power
of the moisture-treated screen A is computed on the
basis of the spectral densities 3A and DB measured
in step 5 above and the gamma value 3.
An organic compound or combination of organic com-
pounds is regarded as satisfying the above Standard ~est
if the result of the determination~in step 6 is that the
fluorescent light-emitting power of screen A incorporat-
ing that c~mpound or combination of compounds is at least
GV.9~6

3L~i3~
25% of tha-t of the non-moisture treated screen B. In the
most preferred embodiment of the invention the organic
compound(s) affording the moisture pro-tection is (are)
such that when such compound(s) is (are) used in screen
A in the Standard q`est -the fluorescent light-emitting
power of screen A is at least 65% and most preferably
a-t least 75% of that of the non-moisture treated screen B.
If screen B in -the S-tandard Test were to be moisture-
treated like screen A before being subjected to the ex-
posure and development mois-ture trea-ted screen B would
show a fluorescen-t power of less than 1~/o relative to
that of the non-moisture treated screen ~.
As already indica-ted a mixture or combination of
organic stabilizing compounds can be employed in aLy
one screen composition.
Preferably use is made of at least one organic com-
pound, which is colourless and upon reaction with the
phosphor yields a colourless hydrophobic reaction product
at the surface of the phosphor particles.
A first class of suitable organic compounds for use
according to this invention comprises organic compounds
wherein reactive hydrogen is directly bound to sulphur,
e.g. in thiols. Preferably thiols are used that contain
a hydrocarbon group of at least 6 carbon atoms. Such
thiols including aliphatic as well as aromatic represen-
tatives have been described by Arthur I.Vogel, ~extbook
of Practical Organic Ghemistry, ~ongmans 3rd ed. (1959~
p. 502. Yery good results are obtained with 1-n-dodecane-
thiol (laurylmercaptan).
A second class of organic compounds for use according
to this invention are organic compounds that contain the
reactive hydrogen in an amino group, i.e. primary or se-
condary amines. Preferably aliphatic primary or secondary
amines are used that contain a hydrocarbon group of àt
G~.9~

- 9 -
least ~ carbon atoms. Especially good results are ob-
tained with 1-n-dodecylamine (laurylamine).
A third class of organic compounds for use according
to this invention are organic compounds that contain
the reactive hydrogen in a carboxyl group. Preferably
aliphatic carboxylic acids are used that contain a
hydrocarbon group of at least 6 carbon atoms. Very good
resul-ts are obtained with dodecanoic acid (lauric acid),
but aliphatic carboxylic acids containing more than one
carboxyl group are considered too, e.g. hexadecylenesucci-
nic acid and octadecylsuccinic acid r
A fourth class of organic compounds for use according
to this invention are organic compounds that contain the
reactive hydrogen in a hydroxyl group, which is preferably
linked to a hydrocarbon group of at least 6 carbon atoms,
such as e.g. in lauryl alcohol, p-t-amylphenol and iso-
hexadecyl alcohol.
~ he hydrocarbon groups as referred to hereinbefore
may comprise substituents that do not enhance the wa-ter-
solubility of the organic compounds beyond the already
given value. Suitable substituents rendering the compounds
more hydrophobic are halogen atoms, e.g. fluorine9 chlo-
rine and bromine, such as e.g. in p-bromophenol and per-
fluorocaprylic acid.
~he above mentioned organic compounds can be used in
combination with metal-organic compounds that are des-
cribed as stabilisers for halide-containing phosphor par-
ticles in the D~-0~ 2~710,497.
~o be mentioned in that respect are, e.g., organotin
compounds and organobismuth compounds. Many of them are
known as hydrogen chloride or hydrogen bromide scavenger
or are known for the slowdown of thermal degradation of
poly(vinyl chloride). ~xamples of such compounds are
~ r1'p he~ylb~,s m~h
triphenylantimony, ~Y~#~r~ and tetraphenyltin.
GV.9gb

- 10 _
~ preferred class of stabilizing organometal com-
pounds for use in combination with the organic compounds
according to -the present invention corresponds to the
following formula :
RmSnXL~ m
wherein :
R is a hydrocarbon group, e.g. an alkyl group,
X is one to three electronegative substituents e.g. oxygen
in substituted form as in an alkoxy or in a carboxylate
group, or is an electronegative sulphur substituent or
a water-repelling sulphur-con-taining substituent linked
through sulphur to -the tin atom e.g. a thioether, a
mercaptide or xanthate group, and
m is 1, 2, or 3, excluding X being three, two or one halo-
gen atom(s) when m is 1, 2 or 3 respectively.
Examples of such compounds are dibutyltin bis(oxo-
octylthioglycolate), also ca]led dibutyltin S,S'-bis(n-
octylmercapto acetate) and
(C4Hg)2Sn--~O-~-R)2 R being -CH ~ C4H9
described as stabilizing agent for polyvinyl chloride by
D.HOSolomon, ~he Chemistry of Organic ~ilm ~ormers, John
Wiley & Sons, IncO New York, p.175 to 177 (1967), and di-
butyltin maleat'e, dibutyltin lauryl mercaptide, and di(n-
octyl)-tin S,S'-bis(iso-octylmercapto acetate) described
by Kirk-Othmer, ~ncyclopaedia of Chemical ~echnology,
2nd compl. revised edition, VolO 21, p.390 (1965) and in
J.Polymer Sci. Part A, Vol. 2 (1964) 1801-1813.
A composition of matter of -the present invention com
prises halide-containing phosphor particles, preferably
inorganic halide-containing phosphor particles, by admix-
ture combined with (a) said organic stabilizing substanca(s)
optionally in a binder medium.
In one process for preparing a composition of matter
GV.9g~

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according to the present invention the halide-containing
phosphor particles are allowed to come in intimate con-
tact with the organic stabilizing substance(s3 in an orga-
nic liquid medium wherein said substance(s) dissolve and
thus treated particles are separated out and dried.
In one process for preparing a radiation conversion
screen according to the presen-t inven-tion the halide-
containing phosphor particles are dispersed in an organie
liquid medium in the presence of (a) dissolved binding
agent(s) and at least one dissolved organic stabilizing
substa~ce. According to one embodiment the dispersing
proceeds in a ball mill.
Preferably the organic stabilizing substance(s) is
(are) combined by admixture with the halide-containing
phosphor particles in a selected phosphor binder layer
combination in an amount suf:Eicient to maintain the
fluorescent light-emitting power of the layer in a moisture
treatment as defined above :Eor screen (~) at a level of
at least 25% and preferably at a level of at least 75% of
the level before said treatment.
~ he amount of organic stabili2ing substance or mixture
of stabilizing substances sui-table for a practically use-
ful increase in stability against moisture of the applied
halide-containing phosphor particles can be determined
by simple tests.
Effective amounts of organic stabilizers, e.g. with
regard to lanthanum oxybromide phosphors, are in the
range of 0.05 to 10 g per 100 g of phosphor. More hygros-
copic phosphors such as cesium iodide phosphors may be
used in conjunction with higher amounts of stabilizer(s).
In the production of a radia-tion conversion sereQn
according to the present invention the dispersion may be
coated and dried on a permanent support, e.g. a cardboard
or resin sheet, or coated on a temporary support to form
GV.9g~

39~
- 12 -
a self-supporting sheet later on. ~he solvent(s) used in
the preparation of the coating composition is (are) nor-
mally evaporated under reduced pressure. An ultrasonic
treatrnent can be applied -to improve the packing density
and to perform the de-aeration of the phosphor-~inder
combination. Before the optional applica-tion of a pro-
tective coating the phosphor-binder layer may be calen-
dered to improve the packing density (i.e. the number of
grams of phosphor per cm3 of dry coating).
Self-supporting screens of this invention can also
be prepared by means of "hot-pressing", excluding the use
of solvent(s) in the manufacture of the screens.
To provide high X-ray efficiency it is preferably
that a minimum amount of binder be employed in the
fluorescent layer. However, the less binding agent the
more brittle the layer, so that a compromise has to be
made. ~he thicker the fluorescent layer of a screen,
the higher its intensification, but the image sharpness
is decreased accordingly so that a balance between speed
and definition has to be sought. ~uitable binders for
use in the preparation of the fluorescent layers are,
e.g., a cellulose acetate butyrate, polyalkyl (meth)acry-
lates, e.g. polymethyl me-thacrylate, a polyvinyl-n-butyral,
a copoly(vinyl acetate/vinyl chloride) and a copoly(acry-
lonitrile/butadiene/styrene) or a copoly(vinyl chloride/vinyl acetate/vinyl alcohol) or mixtures thereof. lhe
preferred binders are halogen-free polymers or copolymers.
Optionally, a light-reflecting layer is provided be-
tween the fluorescent layer and its support to enhance
the exposure of the silver halide emulsion material.
~ o the phosphor-containing layer a protective coating
may be applied preferably having a thickness in the range
of 5 to 25 ~m and be~ng composed of any film-forming poly-
meric material that is phd~graphically inert towards a
GV.~6

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silver halide e~lsion layer.
Polymeric materials sui,-table for that purpose in-
clude~ e.g., cellulose derivatives e.g. cellulose nitrate,
cellulose triacetate, cellulose acetate propionate,
cellulose ace-tate butyra-te, polyamides, polystyrene, poly-
~inyl acetate, polyvinyl chloride, silicone resins, poly
(acrylic ester) and poly(me-thacrylic es-ter) resins, fluori-
nated hydrocarbon resins, and mixtures of the foregoing
materials. Representative examples of various individual
members of these binder materials include the following
resinous materials : poly(methyl methacrylate), poly(n-
butyl methacrylate), poly(isobutyl methacrylate), copoly-
mers of n-butyl methacrylate and isobutyl methacryla-te,
copolymers of vinylidene fluoride and hexafluoropropylene,
copolymers of vinylidene fluoride and triflùorochloro-
ethylene, copol~mers of vinylidene fluoride and tetra-
fluoroe-thylene, terpolymers of vinylidene fluoride, hexa-
fluoropropylene and tetrafluoroethylene, and poly(vinyli-
dene fluoride).
According to a special embodiment -the outer face of
the screen intended for contact with the photographic
silver halide emulsion material contains a solid parti-
culate material that has a static friction coefficie~t
(~) at room temperature (20C) of less than 0.50 on steel.
Antistatic substances may be applied to the screen
to reduce the risk of electrical potential differences
resulting in sparking. ~or example, the screens are
treated with the "A~lI-S~A~" 6 spray, which leaves on
odourless transparent antistatic deposit. AN~I-STA~ is
~rl~
~0 a trade ~ e of Braun ~aboratories Div. Barrett Chemical
Co. Inc., Philadelphia, Pa., U.S.A.
At least a part of the halide-containing phosphor
particles in the present composition of matter are prefera-
bly halide-containing rare-earth metal compounds, in which
GV.9~6

- 14 -
the host metal of the phosphor is a rare-earth metal and
the activa-tor consists of one or more other rare-earth
metals. ~or example, these phosphors contain yttrium,
gadolinium, lanthanum, or cerium as a host metal and at
least one of the metals of the group of terbium, europium,
dysprosium, -thulium, samarium and ytterbium as activator
metal.
Preferred phosphors of this class correspond to one
of the following general formulae :
~a(1 n)Tbn OX
wherein X is halogen such as e.g. chlorine, bromine, or
fluorine, and n is from 0.006 to 0.0001, the halogen being
present preferably in the range of between about the
stoichiometric amount and about 2.5 percen-t differing
therefrom; or
(1-w-y) w y
wherein X is chlorine or bromine
w is 0.0005 to 0.006 mole of the oxyhalide, and
y is 0.00005 to 0.005 per mole of the oxyhalide.
Cerium may replace lanthanum in an amount described in
the U.K.Patent Specification 1,247,602 filed October 9,
1969 by General Electric and Co.
~ he preparation of terbium-activated lanthanum oxy-
chloride and lanthanum oxybromide phosphors emitting
visible light is described~ e.gO, in U.K.Patent Specifi-
cation 1,247,602 mentioned hereinbefore, the ~rench Patent
Specifications 2,021,398 and 2,021,399 both filed October
23, 1969 by General Electric and Co, and the published
German Patent Applications (DE-OS) 1,952,812 filed October
21, 1969 and 2,161,958 filed December 14, 1971 both by
General Electric and Co. Suitable lanthanum oxychloride-
fluoride phosphors are described in the published German
Patent Application (DE-OS) 2,329,396 filed June 8, 1973
by Siemens A.G.
G~.9g6

I'he preparation of lanthanum oxyhalides activated
with terbium and ytterbium is described, e.g., in the
published German Patent Application (DOS) 2,161,958
mentioned hereinbefore.
Oxyhalides of lan-thanum and gadolinium activated
with thulium are described, e.g., for use in radiographic
intensifier screens in the United States Patent Specifi-
cation 3,795,814 of Jacob G.Rabatin, issued March 5, 1974.
An ultraviolet-emi-tting phosphor is barium fluoride
chloride activated with europium(II) as described, e.g.,
in the French Patent Specification 2,185,667 filed May 23,
1973 by Philips Gloeilampenfabrieken ~.V. According to
an embodime~t the present composi-tion of matter is a com-
position wherein at least a part of said phosphor parti-
cles consists of said barium fluoride chloride.
An X-ray image intensifier screen employing rather
hygroscopic sodium-activated cesium iodide is described
in the United States Patent Specifica-tion 3,836,784,
already mentioned hereinbefore. ~ccording to an embodi-
ment the present composition of matter is a compositionwherein at least a part of the phosphor particles is
sodium-activa-ted cesium iodi-de.
I'he thickness of the supported fluorescent layer
may vary within a broad range but is preferably in the
range of 0.05 to 0.5 mm~
~ 'he coverage of the phosphors is, e.g., in the range
of approximately 200 to 800 g/sq.m and preferably approxi-
mately 300 to 600 g/sq.m.
I'he image sharpness obtainable with a fluorescent
screen-silver halide material system can be improved con-
siderably by incorporating a fluorescent light-absorbing
dye, called "screening dye" herein, into the fluorescent
screen material, e.g. into the fluorescent layer or into
a layer adjacent thereto e.g. into a subjacent anti-
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- 16 -
reflectiorl layer. As the oblique radiation covers a
large path in the screen material, it is attenuated by
the screening dye or dyes -to a greater extent than the
radiation impinging normally. ~he term "screening dye"
used herein includes dyestuffs (i.e. coloured substances
in molecularly divided :Eorm) as well as pigments.
Diffuse radiation reflecting from the support of the
fluorescent screen material can be mainly attenuated in
an anti-reflection layer containing the screening dyes
subjacent to the fluorescent layer.
~ he screening dye need not to be removed from the
fluorescent screen material and may therefore be any dye
or pigment absorbing in the emission spectrum of the
fluorescent substance(s). ~hus black substances such as
carbon black particles of an average size of 0.15 to
0.60 ~m incorporated in said anti-reflection layer or the
phosphor layer yield quite satisfactory results.
~ he screening dye(s) is (are) preferably used in the
fluorescent layer e.g. in an amount o~ at least 0.5 mg per
sq.m. When used in the a~ti-reflection layer, however,
the amount of said dye(s) is not limited.
A suitable screening dye for use in the fluorescent
screens emitting in the green range (500 to 600 nm) of the
visible spectrum is, e.g., Neozapor~ ~ire Red (C.I. Solvent
Red 119), an azochromium rhodamine complex. Other suitable
screening dyes are C.I. ~olvent Red 8, 25, 30, 31, 32, 35,
71, 98, 99, 100, 102, 109, 110, 118, 124 and 130.
~ he non-self-supporting phosphor-binder composition
may be coated on a wide variety of supports, e.g. cardboard
and plastic ~ilm, e.g. polyethylene terephthalate film.
A support used in a fluorescent screen of the prese~t in-
vention may be coated with (a) subbing layer(s) to improve
the adherence of the fluorescent coating thereto.
Screens according to the present invention may be
GV.9~ ~ PF ~R~

- 17 -
used in conjunction with light-sensitive silver halide
materials emulsion-coated on one or both sides of the
support.
~ he following examples illus-trate the present inven-
5 tion.
_xam~le 1
Preparation of screen A
A mixture consisting of 100 g of terbium-activated
lanthanum oxybromide phosphor, 0. 5 g of lauric acid as
stabilizing compound~ 12.5 g of poly(vinyl-n-butyral)
still containing ~2% by weight of non-acetalized vinyl
alcohol units and having an average molecular weight of
50,000, and 48 g of ethylene glycol monomethyl ether were
ball-milled to a fineness of grind corresponding with
7 NS Hegman fineness of grind measured with the Hegman
gauge as specified in AS~M D1210. ~he dispersion obtained
was filtered and after de-aeration coated onto a baryta-
coated paper of 290 g per sq.m at a coverage of 500 g per
sq.m to form said screen A.
20 Preparat-ion of screen B
~ he X-ray image intensifying screen (B) was manufac-
tured as described for screen (A) with the difference that
the stabili~ing compound was omitted from the composition
of the screen.
25 Moisture treatment
_~.
~ he moisture treatment of screens (A) and (~) pro-
ceeded by covering congruently the phosphor coating of
each of the screens (A) and (B) with a wet circular plece
of filter paper having a weight of 1.355 g in dry state,
a diameter of 15 cm, and a water content of 3.100 g.
Subsequently, -the covered screens (A) and (B) were sepa-
rately packed air-tight in a polyethylene bag and kept
at 60C for 64 h in a ventilated cabinet. ~he screens (A)
and (B) were removed then from the bag and after removal
of the fil-ter paper dried in the air for 30 min at 80C.
GV.996

- 18 -
X-ray exposure and developmen-t
The thus moisture-treated screens (A) and (B) and a
screen (B1) which was like screen B but was untrea-ted with
moisture, ~?ere exposed to X-rays in contact with a CUP.IX
RP1 film (Curix is a trade mark of the Applicant for a
medical X-ray film). The exposure was e:Efec-ted to such
a degree that after development for 23 s at 35C in Agfa-
Gevaert's hardening developer G 138 containing hydroquinone
and 1-phenyl-3-pyrazolidinone as developing agents and
glutaraldehyde as a hardener the area of the silver halide
material exposed in contact with the untrea-ted screen (B1)
showed a transmission spec-tral clensity of 1082 above fog~
After ~radually increasing exposures with screen (B ) of
the above film material and said development of the film
as described a silver image with a gamma (~ ) of 3 is
obtained~
'~he transmission spectral denslties obtained with the
moisture-treated screens (A) and (B) were 1.76 and zero
above fog respectively~
~he actual loss in fluorescence power of screen (A)
was computed as follows :
density (~ D) = 1.82 - 1.76 = 0.06
~ log exposure (~ log E) = ~D = 0306 = 0.02
antilog 0.02 = 1.05 ; 1/1.05 = 0.95
100% - 95% = 5%.
A usable result was also obtained by replacing lauric
acid by a same amount of 1-n~dodecylamine.
Pre aration of screen I
- 5 g of a 40% by weight solution in toluene of E~ACI~E
B 2044 (ELVACI~ 2044 is a trade r~ of E.I~ du Pont de
Nemours & Co. (Inc.), Wilmington, Del., U.S.A., for a
poly-n-butyl methacrylate)
- 100 g of LaOBr: 0.02 ~b: 0.0005 Yb phosphor particles
GV.9~6

- 19 -
prepared according to published German Patent Specifi-
cation 2,161,958,
- 0.5 g of the stabilizing compound : laurylmercaptane,
and
- 251.2 g of toluene were ball-milled for 4 h, whereupon
a further amount of 10.5 g of EI~ACIrlE 2044 (trade ~ff~e)
was added and ball-milling was continued up to a Hegman
fineness of grind of 7 NS (average phosphor particle
size 7 ~m) measured with the Hegman gauge as specified
in ASr~M D1210.
r~he dispersion ob-tained was coated at a coverage of
500 g per sq.m of phosphor on a subbed polyethylene tereph-
thalate support and dried.
~e ~ g~
Screen II was prepared in the same way as described
for screen I with the differencej however, that the sta-
bilizing compound was omi-tted from the composition.
Moisture treatment
~ . . ~
Circular pieces of screen I and screen II each of
them having a diameter of 15 cm were separately covered
congruently with a wet circular piece of filter paper
having a weight of 1.355 g in dry state, a diameter of
15 cm, and a water content of 3.100 g. Each of the thus
co~ered screens was packed air-tight separately in a poly-
ethylene bag and kept at 60C in a ventilated cabinet for64 h. Subseguently, the covered screens were removed from
the polye-thylene bag and the pieces of screens I and II
after separation from the filter paper were dried in the
air for 30 min at 80C.
~
rIhe moisture-treated screens I and II and an untreated
screen II were exposed to X-rays in contact with a CURIX
(trade mark) RP1 film. r~he e~posure was effected to such a
degree that after development for 23 s at 35C in Agfa-
GV.996

- 20 _
Gevaert's haldening developer G 138 containing hydroqui-
none and 1-phenyl-3-pyrazolidinone as developing agents
and glu-taraldehyde as a hardener the area of the silver
halide material exposed in contact with the untreated
screen II'showed a transmission spectral density of
1.25 above fog.
Computed from the difference in density obtained
with the moisture-treated screen I and non-moisture-
trea-ted screan II' the ac-tual loss in fluorescence power
of screen I was 7.9 %.
Example 3
Preparation_of_scre__ P
A mixtu~e consisting of 100 g of terbium-activated
lanthanum oxybromide phosphor, 0.5 g of lauryl alcohol
as stabilizing compound, 12.5 g of poly(vinyl-n-butyral)
s-ti]l containing 12% by weigh-t of non-acetalized vinyl
alcohol units and having an average molecular weight of
50,000 and 48 g of ethylene glycol monomethyl ether were
ball-milled to 7 NS Hegman fineness of grind measured with
the Hegman gauge as specified in AS~M D1210. ~he disper-
sion obtained was filtered and after de-aeration coated
onto a baryta-coated paper of 290 g per sq.m at a coverage
of 150 g of phosphor per sq.m to form screen P.
~he phosphor layer was overcoated with a protective
coating from a 7.5% solution in ethylene glycol monomethyl
ether of cellulose acetate butyrate having a degree of
substitution (DS) of ace-tyl 1.31 and a DS of butyryl of
1.51. ~he dried protective coa-ting had a coating weight
of 10 g per sq.m.
Preparation of screen Q
The X-ray image intensifying screen Q was manufactured
as described for screen P with the difference that the
stabilizing compound was omitted from the composition of
the screen.
GV.9~

- 21 -
Preparation of screen R
~ he X-ray image in-tensifying screen R was manufac-
tured as described for screen P with the difference that
before coating the oxybromide phosphor dispersion was
mixed with a calcium tungstate phosphor dispersion pre-
pared as described for the lanthanum oxybromide phosphor
dispersion of screen P wi-th the only difference that the
oxybromide phosphor was replaced by a same amount of cal-
cium tungsta-te. ~he calcium tungstate phosphor dispersion
was added in an amoun-t such -that -thefinal dispersion con-
tained the oxybromide phosphor and calcium tungstate phos-
phor in a ratio of 1:2.
~ he phosphor mixture dispersion was coated on the
same support as described for screen P at a phosphor
mixture coverage of 150 g of terbium-activated lanthanum
oxybromide phosphor and 300 g of calcium tungstate per sq.m.
Moisture treatment
_
~ he moisture treatment of screens P, Q and R proceeded
by incuba-tion in a cabinet having inside an atmosphere
of 85% relative humidity at 20C. Said incubation treat-
ment was effected for a period of 2 weeks. ~fter that
period the fluorescence power of screen Q was completely
lost and screen P showed randomly distributed spots and
small craters. ~creen R did not show any trace of dete-
rioration. When screens P and R were X-ray exposed in
contact with separate strips of the same silver halide
emulsion film the developed film s-trip exposed in combi-
nation with screen P showed more than 100 white spots per
s~.dm whereas the developed film strip which wa~ exposed
in contact with screen R did not show any spots a-t all
and wa-s evenly blackened.
~ he ratio of -the intensification factors of screens P
and R was 1:1.
GV.9g6