MATERIAUX THERMOSENSIBLES COMPRENANT UNE SUBSTANCE A REACTION RETARDEE ET UN COLORANT ANTI-HALO OU FILTRE

HEAT SENSITIVE MATERIALS INCLUDING A HEXAARYLBIIMIDAZOLE DIMER AND AN ANTIHALATION OR FILTER DYE

Abrégé anglais

Abstract Or the Disclosure
A heat bleachable material comprises (i) at
least one hexaarylbiimidazole with (ii) at least one
dye, especially an antihalatlon or filter dye, that is
reactive with the product of the hexaarylbiimidazole formed
upon heating the material to a temperature above about
90°C. This provides a material that becomes at least 40%
colorless within about 20 minutes, typically within about 30
seconds, upon heating to a temperature as described. The
dye-containing material is especially useful for antihalation and
filter purposes in a photographic element. The material can be a
heat bleachable dye layer of a photothermographic element.
The heat bleachable dye layer can also be useful in a
thermographic element.

Revendications

WHAT IS CLAIMED IS:
1. In a photographic element comprising (a) a
support having thereon (b) a photosensitive component layer
comprising photosensitive silver halide, a photosensitive
diazo imaging material, a photosensitive dye or a photo-
sensitive combination of a photoreductant and a cobalt
amine complex; and, in the support or on the support in a
layer separate from said photosensitive component layer,
(c) an antihalation or filter component, the improvement
wherein said antihalation or filter component comprises,
in reactive association, (i) at least one hexaarylbiimida-
zole with (ii) at least one antihalation or filter dye that
is reactive with the product formed upon heating of said
hexaarylbiimidazole to a temperature of at least about
90°C, and wherein said antihalation or filter component
becomes at least 40% colorless within less than about 20
minutes upon heating to a temperature of at least about
90 °C.
2, A photographic element comprising (a) a
support, having thereon (b) at least one photosensitive
layer comprising photosensitive silver halide and, in the
support or on the support in a layer separate from said
silver halide layer, (c) at least one antihalation or
filter component comprising, in reactive association,
(i) at least one hexaarylbiimidazole with (ii) at least
one formazan antihalation or filter dye that is reactive
with the product formed upon heating of said hexaaryl-
biimidazole to a temperature of at least about 90°C, and
wherein said antihalation or filter component becomes at
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least about 40% colorless within less than about 20
minutes upon heating to a temperature of at least about
90°C.
A photographic element as in claim 2 wherein
said antihalation or filter component is present in said
support.
4. A photographic element as in claim 2 wherein
said antihalation or filter component is present in an
antihalation layer on said support.
5. A photographic element as in claim 2 also
comprising a polymeric binder.
6. A photographic element as in claim 2 also
comprising a silver halide developing agent in reactive
association with said photosensitive silver halide.
7. A photographic element as in claim 2 also
comprising a sulfonamidophenol silver halide developing
agent in reactive association with said photosensitive
silver halide.
8. A photographic element as in claim 2 wherein
said antihalation or filter component becomes at least 90%
colorless within less than about 30 seconds upon heating to a
temperature of at least 120°C.
9. A photographic element as in claim 2 wherein
said antihalation or filter component also comprises up to
about 20 mg of l-naphthoic acid per square foot of support.
10. A photographic element as in claim 2 wherein
said antihalation or filter component comprises an antihalation
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layer comprising a maleic anhydride-styrene copolymer binder
on said support.
11. A photographic element as in claim 2 wherein
said hexaarylbiimidazole is an oxidative arylimidazole dimer
of a compound represented by the formula:
<IMG>
wherein R and R' are individually selected from alkyl containing
1 to 4 carbon atoms and hydrogen.
12. A photographic element as in claim 11 wherein
R' is isopropyl and R is hydrogen.
13. A photographic element as in claim 2 wherein
said formazan dye is a triarylformazan dye.
14. A photographic element as in claim 2 wherein
said antihalation or filter dye comprises a combination of
at least two dyes.
15. A photographic element comprising (a) a
support having thereon (b) at least one silver halide
photosensitive layer, and (c) at least one antihalation
layer comprising, in reactive association, (i) at least one
oxidative arylimidazole dimer of a compound represented
by the formula:
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<IMG>
wherein R and R' are individually selected from isopropyl and
hydrogen, with (ii) at least one triarylformazan antihalation
dye, and (iii) a polymeric binder comprising a maleic
anhydride-styrene copolymer, wherein said antihalation layer
becomes at least about 90% colorless within less than about
30 seconds upon heating to a temperature of at least about 120°C.
16. A photographic element comprising (a) a
support, having thereon (b) at least one non-silver photo-
sensitive layer comprising a photosensitive diazo imaging
material or a photosensitive combination of a photoreduc-
tant and a cobalt amine complex and, in the support or on
the support, (c) at least one antihalation or filter com-
ponent comprising, in reactive association, (i) at least
one hexaarylbiimidazole with (ii) at least one formazan
antihalation or filter dye that is reactive with the product
formed upon heating of said hexaarylbiimidazole to a
temperature of at least about 90°C, wherein said anti-
halation or filter dye component becomes at least about
40% colorless within less than about 20 minutes upon
heating to a temperature of at least about 90°C.
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18. A photographic element as in claim 16
wherein said non-silver photosensitive layer comprises
a quinone photoreductant.
19. A colored, heat bleachable antihalation
or filter dye composition comprising (i) at least one
hexaarylbiimidazole with (ii) at least one antihalation
or filter dye that is reactive with the product formed
upon heating of said hexaarylbiimidazole to a temperature
of at least about 90°C, and wherein said composition
becomes at least about 40% colorless within less than
about 20 minutes upon heating to a temperature of at
least about 90°C.
20. A colored, heat bleachable antihalation
or filter dye composition as in claim 19 comprising (i)
at least one hexaarylbiimidazole with (ii) at least one
formazan antihalation or filter dye that is reactive
with the product formed upon heating of said hexaaryl-
biimidazole to a temperature of at least about 90°C,
wherein said composition becomes at least about 90%
colorless within about 20 minutes upon heating to a
temperature of at least about 90°C.
21, A colored, heat bleachable antihalation
or filter dye composition as in claim 19 also comprising
a polymeric binder.
22. A colored, heat bleachable antihalation
or filter dye composition as in claim 19 wherein said
composition becomes at least 90% colorless within less
than about 30 seconds upon heating to a temperature of
at least 120°C.
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23. A colored, heat bleachable antihalation
or filter dye composition as in claim 19 also comprising
a polysulfonamide binder.
24. A colored, heat bleachable antihalation
or filter dye composition as in claim 19 also comprising
a poly(ethylene-co-1,4-cyclohexylenedimethyle-1-
methyl-2,4-benzene disulfonamide) binder.
25. A colored, heat bleachable antihalation
or filter dye composition as in claim 19 also comprising
a maleic anhydride-styrene copolymer binder.
26. A colored, heat bleachable antihalation
or filter dye composition as in claim 19 also comprising
a poly(vinyl butyral) binder.
27. A colored, heat bleachable antihalation
or filter dye composition as in claim 19 wherein said
hexaarylbiimidazole is an oxidative arylimidazole dimer
of a compound represented by the formula:
<IMG>
wherein R and R' are individually selected from alkyl
containing 1 to 4 carbon atoms and hydrogen.
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28, A colored 3 heat bleachable antihalation
or filter dye composition as in claim 27 wherein R' is
isopropyl and R is hydrogen.
29. A colored, heat bleachable antihalation
or filter dye composition comprising a combination of
(i) at least one oxidative arylimidazole dimer of a com-
pound represented by the formula:
<IMG>
wherein R and R' are isopropyl or hydrogen and at least one
of R and R' is isopropyl, with (ii) at least one
formazan antihalation dye, and (iii) a polymeric binder
comprising a maleic anhydride-styrene copolymer, wherein
said combination becomes at least about 90% colorless within less
than about 30 seconds upon heating to a temperature of at least
130°C.
30. A photothermographic element comprising (a) a
support having thereon (b) at least one layer comprising (1)
photosensitive silver halide, with (2) an image-forming
combination comprising (i) an organic, silver salt oxidizing
agent with (ii) organic reducing agent for said organic,
silver salt oxidizing agent, and (3) a polymeric binder,
and (c) an antihalation component comprising a combination,
in a layer on the support, of (A) at least one hexaaryl-
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biimidazole with (B) at least one antihalation dye that is
reactive with the product formed upon heating of said
hexaarylbiimidazole, upon heating to a temperature of at
least about 90°C, and wherein said combination of (A) with
(B) becomes at least about 90% colorless within about 20
minutes upon heating to a temperature of at least about
90°C.
31. A photothermographic element as in claim 30
wherein said antihalation component (c) is an antlhalation
layer between said support and said layer (b) comprising
photosensitive silver halide.
32. A photothermographic element as in claim 30
wherein said antihalation component (c) is an antihalation
layer on the side of said support opposite the side containing
said layer (b) comprising photosensitive silver halide.
33. A photothermographic element as in claim 30
wherein said antihalation component (c) also comprises up to
about 20 mg of l-naphthoic acid per square foot of support.
34. A photothermographic element as in claim 30
wherein said antihalation component (c) is an antihalation
layer also comprising a polymeric binder on said support.
35. A photothermographic element as in claim 30
wherein said antihalation component (c) is an antihalation
layer comprising a polysulfonamide binder on said support.
36. A photothermographic element as in claim 30
wherein said antihalation component (c) is an antihalation
layer comprising a poly(ethylene-co-1,4-cyclohexylene-
dimethylene-1-methyl-2,4-benzene disulfonamide) binder
on said support.
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37. A photothermographic element as in claim 39
wherein said antihalation component (c) is an antihalation
layer comprising a maleic anhydride-styrene copolymer
binder on said support.
38. A photothermographic element as in claim 30
wherein said antihalation component (c) is an antihalation
layer comprising a poly(vinyl butyral) binder on said support.
39. A photothermographic element as in claim 30
wherein said hexaarylbiimidazole is an oxidative arylimidazole
dimer of a compound represented by the formula:
<IMG>
wherein R and R' are individually selected from alkyl containing
1 to 4 carbon atoms and hydrogen.
40. A photothermographic element as in claim 39
wherein R' is isopropyl and R is hydrogen.
41. A photothermographic element as in claim 30
wherein said antihalation dye is a triarylformazan dye.
42. A photothermographic element comprising (a) a
support having thereon (b) at least one gelatino silver
halide photosensitive layer comprising (i) photosensitive
silver halide, (ii) a gelatino binder, (iii) a base-release
agent, (iv) an image stabilizer precursor, and (v) a silver
halide developing agent, and (c) an antihalation layer
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comprising a combination of (A) at least one hexaarylbiimidazole
with (B) at least one antihalation dye that is reactive with
the product formed upon heating of said hexaarylbiimidazole
upon heating to a temperature of at least about 90°C and (C)
a binder, and wherein said combination of (A), (B) and (C)
becomes at least 40% colorless within about 20 minutes upon
heating to a temperature of at least about 90°C.
43. A photothermographic element as in claim 42
wherein said antihalation layer (c) is between said support
and said layer comprising photosensitive silver halide.
44. A photothermographic element as in claim 42
wherein said antihalation layer (c) is on the side of said
support opposite the side containing said layer comprising
photosensitive silver halide.
45. A photothermographic element as in claim 42
wherein said antihalation layer (c) also comprises up to
about 20 mg of l-naphthoic acid per square foot of support.
46. A photothermographic element as in claim 42
wherein said binder (c) in said antihalation layer (c) comprises
a polysulfonamide.
47. A photothermographic element as in claim 42
wherein said binder (c) in said antihalation layer (c) comprises
poly(ethylene-co-1,4-cyclohexylene-dimethylene-1-methyl-2,4-
benzene disulfonamide).
48. A photothermographic element as in claim 42
wherein said binder (c) in said antihalation layer (c) comprises
a maleic anhydride-styrene copolymer binder.
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49. A photothermographic element as in claim 42
wherein said binder (c) in said antihalation layer (c) comprises
poly(vinyl butyral).
50. A photothermographic element as in claim 42
wherein said hexaarylbiimidazole (A) is an oxidative
arylimidazole dimer of a compound represented by the formula:
<IMG>
wherein R and R' are individually selected from alkyl
containing 1 to 4 carbon atoms and hydrogen.
51. A photothermographic element as in claim 50
wherein R' is isopropyl and R is hydrogen.
52. A photothermographic element as in claim 42
wherein said antihalation dye (B) is a formazan dye,
53. A process of (a) developing an image in an
exposed photothermographic element as defined in claim 30
and (b) changing the antihalation component in said element
from colored to at least 40% colorless comprising heating
said element to a temperature of at least about 90°C until
said image is developed and said antihalation component is
changed from colored to at least 40% colorless.
54. A process of (a) developing and stabilizing
an image in an exposed photothermographic element as defined
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in claim 42 and (b) changing the antihalation component in
said element from colored to at least 40% colorless comprising
heating said element to a temperature of at least 90°C until
said image is developed and stabilized and said antihalation
component is changed from colored to at least 40% colorless.
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Description

~ack~round of the In~ention
Field o~ the In~ention
The present invention rela-tes to an element,
- especiall~ a photographic element, having at least one la~er
that changes its electromagnetic absorption characteristics
upon application of heat. l'his layer is useful, for example,
as a ~ilter la~er or an antihalation ~Layer in a photographic
element, such as a photothe~mographic element. The layer
is also useful in a thermographic recording element.
State o~ the Art
~ variety o~ phctographic materials are known which
can be processed by immersion in various processing
solutions or baths. It is well known to provide di~ferent
-filter layers, including fllter overcoat layers,
filter interlayers and antihalation layers in such elements
to provide improved photographic reproduction. The
filtering capability or antihalation capability of
these layers i.s generally removed during processing o~
these elements by one of the processing solutions or baths.
This provides a processed element that is transparent to
the desired region of the electromagnetic spectrum, typicalIy
the visible region.
Imaging elements are also known which can be processed3
after imagewise exposure, simply by heating the element. These
elements include known heat developable photographic elements~
also known as photothermographic elements. It is desirable
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,., ~

that heat developable elemen-ts, such as heat developable photo-
graphic films, have an antihalation layer or filter layer,
especially to pro~ide improved microimaging capability. In most
cases, these filter layers or antihalation layers must be rendered
substantially transparent upon heat processing in order to avoid
use of processing baths or solutions.
The antihalation layer of a photographic element helps
to prevent light that has passed through the radiation sensitive
layer from reflecting back into the light sensitive layer. If
this undesirable reflection is not prevented, the reflected light
can reduce the sharpness of the resulting imaye. Antihalation
layers, and filter layers, have been suggested for use with heat
developable photographic elements.
~ ntihalation layers in heat developable materials are
known which change from colored to colorless on exposure to heat
or light. No separate activating component is used in such an
antihalation layer. The dyes described provide antihalation
protection; however, the dyes generally require higher tempera-
tures than desired before they change from colored to colorless.
Another antihalation layer is known in a heat developable photo-
graphic element that contains an acid component of a dye which
is neutralized by a heat generated base. This is described, for
instance, in U.S. Patent 3,769,019 of Wiese et al. Decoloriza-
tion of the described dye takes place by removal of an acid por-
tion by heat. A problem with this antihalation material is that
the decolorization form of the dye is not always as permanent
as desired. The decolorized form changes back to a colored form
which adversely affects the developed image. This can occur
within an undesirably short period of time. `-
~ 3 _
~ ~ ..~.
, ~
. . ,

f~
Photobleachable antihalation layers containing dyes
that are photobleachable are also known. It is often disadvan-
tageous, however, to have a photosensitive antihalation layer, as
a post-process light bleaching step is needed, an additional
processing operation.
~ ntihalation layers have also been used both for
vesicular and diazo imaging films. These films, however, involve
exposure of the antihalation layer to light to inactivate the
material and do not use heat to bleach the antihalation layer.
Typically, layers that can be useful as antihalation
layers, or filter layers~ in a photothermographic element, can
also be useful alone on a support to provide an element that is
useful for thermographic imaging purposes. That is, the element
can be imagewise heated to provide heat bleaching in the image-
wise exposed areas. In this method of imaging any color change
can be useful to form an image. For example, a substantially
colorless dye precursor can be imagewise heated to form a positive
colored image. A colored dye can also be imagewise thermally '~
exposed to form a colorless material to provide a neyative image.
A variety of thermographic materials are known that can use this
concept. Brief imagewise heating of the element causes migration
of the reactants which results in decolorization in the imagewise
heated a~rea. Many thermographic elements are also useful for
making reflex copies, writing with a heated stylus or imagewise
exposure with a laser. Imagewise changing of a formazan dye from
colored to colorless with a reducing agent is also known. This is
described, for example, in Resea'rch D'isclosure, October 197
.
. .

Item 12617, pages 12-30, published by Industrial Opportunities
Ltd., Home~ell, ~Iavant~ Hampshire3 PO9 l:E~ UK. There has .
been a continuin~ need, however, to provide new and improved
combinations of materials ~or thermo~raphic imaging with dyes.
mis need has been especially true ~or materials which are
more permanently changed in color to provide more stable
images.
A variety of hexaarylbiimidazole compounds are
known in the.imaging elements in which a colorless compound
is photolytically changed to a colored compound in the
imagewise exposed areas. Imaging materials which embody
hexaarylbiimidazole compounds are known which involve
what is described as a free r~dical imaging mechanism
such as described in U.S. Patent 3,390,99~ of Cescon,
issued July 2, 1968. Formation of a colorless layer
is not described for a heat developable photographic
element comprising a formazan dye with a hexaal^ylbiimidazole
compound.
Each of the described elements having a heat
bleachable layer, especially the photothermographic elements
containing a heat bleachable filter or antihalation layer,
have at least o.ne of the disadvantages: (1) undesirably
high temperatures are required to bleach the layer; (2) in
many cases e~en when the dye is bleached it is not adequately
stable and has a tendency to form undesired stain or
discoloration on prolonged post process keeping; and
(3) the choiGe of suitable dyes is undesirably limited .-:
for antihalation and filter layer purposes. ~ need has also
existed for antihalation layers that pro~ide a desired
neutral cQlor for use in photothermographic films.
-- .
.
', ' ~

Summary of the Invent _n
It has been found according to the i.nvention that
the described improvements are provided in a photographic
element comprising (a) a support having thereon (b) a photo-
sensitive componen* and, in the support or on the support,
(c) an antihalation or filter component that comprises,
in reactive association, (i) at least one hexaarylblimidazole,
as described herein, with (ii) at least one antihalation
or filter dye that is reactive with the product of the
descr'lbed hexaarylbiimidazole formed upon heating to a
temperature of at least about 90C, and wherein the
antihalation or filtered component becomes a-t least 40~,
preferably at least 90~, colorless within.less than about
20 minutes, typically within about 0.5 minutes, upon heating
.-to a temperature of at least about 90C. The described
antihalation or filter component is especially advantageous
'because of the post-processing stability of the component,
the speed with which the~layer becomes at least 40~ colorless
upon heating, and exhibits good shelf li~e storage stability.
These advantages are especially apparent in a
photographic element according to the in~ention comprising
(a) a support, especially a transparent film support having
thereon, (b) at least one photosensitive layer and,.in the
support or.on the support, (c) at least one antihalation
component comprising, in reactive association, (i) at least
one hexaarylbiimidazole with (ii) at least one formazan
antihalation dye, wherein the antihalation compone.nt
becomes at least about 40~g and preferabl~ at least 90~,
colorless within less than about 20 min~tes upon heating
to a temperature of at least about 90C.
I'he colored heat bleachable material according
to the invention is useful in a variety o~ ways to provide
improved imaging. Ihese advantages are embodied accord:ingly

in a colored, heat bleachable composition comprising, in reactive
association, (i) at least one hexaar~lbiimida~ole, as described,
with (ii) at-least one dye that is reactive with the product
of the described hexaar~lbiimidazole upon heating to a
. temperature of at least about 90C, typically at least about
120C, and wherein the heat bleachab:le cornposition becomes
essentially colorless within less than about 20 minutes,
typically within less than about 30 seconds, upon heating
to a temperature of at least about 90C. One embodiment
of this aspect of the inven~ion is a thermographic element
comprising a support ha~ing thereon at least one layer
comprising a combination of (i~ at least one hexaarylbiimidazole,
as described, with (ii) at least one dye, especially at least
one formazan dye, that is reactive with the product of the
hexaarylbiimidazole upon heating to a temperature of at least
.
about 90C and (ii) a binder, and wherein the combination
becomes at least ~O~o, and preferably at least 90~ colorless
within less than 30 seconds upon heating to a temperature
of at least 120C. .
Detailed Descriptio;n of the Invent~on
A variet~ of hexaar~lbiimidazole compounds are useful .
in a materlal according to the invention. These
hexaarylbiimidazole compounds also describe~ herein as
oxidative ar~limidazoyl dimers, are known comp.ounds and can be
prepared by methods know.n in the art. For instanc:e,
hexaarylbiimidazoles can be prepared by means of an inter~acial
oxidation of the parent triarylimidaæole using potassium
ferricyanide as an oxidant. Typical hexaarylbiimi.dazole
~ compounds ~hat are useful according to the invention are
described, for example3 in and can be selected ~rom the
following patents: U.S. 3,734,733 of Poot et al, issued
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~''' '
'

Qg~
....
May 22, 1973; U.S 3,390,997 o~ Read, lssued July 2, 1968;
U.S~ 3,383,212 of MacLachlan, issued May 14, :L968, U.S.
3,445,234 of Cescon et al, issued May 20, 1969; U.S.
3,395,018 of Read, issued July 30, 1968; U.S. 3,390,994
of Cescon et al, issued July 2, 1968, U~S. 3,615,481 of
Looney, issued October 26, 1971; U.S. 3,666,466 o~ Strilko,
issued May 30, 1972; U.S 3,630,736 of Cescon/ isstued
December 28, 1971; and U S. 3,533,797 of James et al, issued
October 13, 1970
10Typical examples of useful hexaarylbiimidazole
compounds include oxidative 2,4,5-triaryllmidazolyl dimers
in which the aryl groups are ~elected from ~isopropylphenyl,
~-methoxyphenyl, p-n-butylphenyl, ~-methylphenyl and
p-ethylphenyl.
As especially useful compound is an oxidative
arylimidazoyl dimer of a compound represented by the formula:
R
(I) ~
R' ~ R'
wherein R and R' are alkyl containing 1 to 4 carbon atoms, ~:
such as methyl, ethyl, propyl and butyl, or hydrogen.
~0If desired, a combination o~ hexaarylbiimidazole
compounds can be useful, An example o~ such a combination
is the combination o~ compounds, within structure (I), (a)
wherein R and R' are hydrogen with (b) wherein R and Rl are :
isopropyl .
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, ~
~D~.~r~ -~y~y~ t7~ ~.. y.~ y.~lYt.~,t~r~,tY.trt.~,~Y~t~Jw~ sY~ Y/~t~r~r~ ~ns~r~ nt~
.

Selection of an optimum hexaarylbilmidazole compound
or combination o~ such compounds will depend upon such factors
as the particular antihalation or filter dye or dyes to be
used, processing conditions, desired degree of bleaching in
the layer containing the dye or dyes~ solubility character-
istics of the components and the like.
A variety of dyes and dye precursors can be use~ul
according to the invention with the described hexaarylbiimida-
zole compounds. Any dye or dye precursor can be used according
to the invention which changes its color, i.e., changes its
electromagnetic radiation absorption characteristics, upon
reaction with what are believed to be free radicals provided
upon heating the described hexaarylbiimidazole compounds. For
antihalation layer purpose6, ~or example, it is desirable that
the heat bleacha~le layer have substantially uniform absorp-
tion in the spectral region in which the imaging composition
is sensitiveO The antihalation dye or dye precursor should
also be changed to the extent that at least about 40 percent~
and preferably at least 90 percent7 of the layer is changed
~rom colored to colorless or the layer has substantially no
optical density upon being heated to at least 90C.
A variet~ of dyes are known which are bleachable
or converted to a colorless form. Formazan dyes and azo dyes
are examples of dyes that are useful.
Especially use~ul antihalation dyes are formazan ~ ;
dyes. Useful formazan dyes are represented, for example,
by the structure:
~ ~N=N~R3
R - C~
N-N-~I
~ R4
formazan dye
wherein:
_ 9 _

a~
R2 is alkyl or aryl, such as methyl, ethyl, hexyl
or phenyl3 p-nitrophenyl and dimethoxyphenyl,
R3 is aryl, preferably phenyl, including substi-
tuted phenyl, such as ~-nitrophenyl, ~ methoxyphenyl and
anthraquinonyl; and
R4 is aryl, prefera~ly phenyl, including substituted
phenyl, ~-nitrophenyl, ~-me~hoxyphenyl and anthraquinonyl.
Especially useful formazan dyes include, for
instance:
1. 1,3,5-triphenylformazan
2. 1-(4-chlorophenyl)-3,5-diphenylformazan
3. 1-p-nitrophenyl~3,5-(diphenyl)formazan
4. 1,5-diphenyl-3-methylformazan
5. 155-diphenyl-3-(3-iodophenyl)formazan
6. 1,5-diphenyl-3-(2-naphthyl)~o~nazan, and
7?~ 1-(2-carboxyphenyl) ~3,5-diphenylformazan.
Other useful formazan dyes are described, for example, in
Research Disclosure, October 1974, Item 12617~ pages 12-30,
published by Industrial Opportunities Ltdo~ Homewell,
2\0 Havant, Hampshire, PO9 lEF, UK. U~S. Patent 3,227,556 of
Oliver and G~tes, issued January 4, 1966; U.S. 3,050,3~3
of Macdonald, issued August 21, 1962, and Chemical Reviews,
1955, beginning at page 356. Useful formazan dyesg as des-
cribed, also include metallized formazan dyes.
Combinations of formazan dyes can be especially
useful to provide the desired degree of absorption. An
example of a combination of formazan dyes is triphenyl-
~ormazan with 1 (p-nitrophenyl)-3-methyl-5-phenyl~ormazan.
- 10 -
~.--,? ~r? '~~~ ? .r.r~ 7~ ' 7~ ?'~ 7~'~,~? ,~,~r~?, ~ ?~ ~, r ~ 1 r 7r~ ? ~l~r?r~? ?~ ??r ,~r r~7~?? '~7 ?~? ?~,~? '-~ ~ ~ .y~ ? ~
~' ', ,

$~
invention, the imagewlse heating means can be any heating
means which provides a visi~le image in the heated areas of'
~he element. This'can be a simple hot plate, infrared heating
means and the li~e.
, A visible image can be developed in a heat
developable photographic material according to the invention
within a short time after imagewlse exposure merel~ b~
uni~ormly heating the heat developable material to moderatel~
elevated temperatures. For example, the heat developable
photographic element can be heated after imagewise exposure
to a tempe:rature within the range which provides development - ~"
of the latent image and a].so provides the necessar~
temperature to cause the antihalation or fil~er layer to
change from colored to colorless. This tempera~ure is within ; '
'''the range of about 90C to about 250C, such as within
. .
the range o~ about 110C to about 200~C. ~Ieating is
t~pically carried out until a desired image is developed
and until the antihalation or filter layer is bleached to a
desired degree~ This,heating time is typically a time within
about 1 second to about 20 minutes, such as'about 1 second to
about 90 seconds. The heat developable photographic material
accord~ng to the invention is typically heated to a temperat~re
within the range of about 90C to about 250C for about
1 second to about 20 minutes.
A,nother embodiment of the invention is a proces's
of (a) developing'an image in an exposed photothermographic
element as, described and (b) changing the antihalatiorl component
in the described element from colored to at least ~0~ and
preferabl~ at least 90~, eolorless comprising heating the
element tQ a temperature of at least about 90C until the image
is developed and the antihalation component is changed from
colored to at least L~o~, and preferably at least 90~, colorless.
, - 25

I~e hea~ developable photosensit:ive ma-terLals
according to the invention can be useful foY foYm:Lng a
negative or a positive image. Ihe formation of a negative
or positive image can depend, for example, pr:imarily upon
the selection of the particular photosensitive silver ha]ide.
One class of useful photosensitive si:lver halide materials
is the class of direct positive photographic silver halide
materials designed to produce positive images.
Processing according to the invention is usually
carried out under ambient conditlons of pressure and humidity.
Pressures and humi~ity outside normal atmospheric conditions
can be emp]o~ed if desired, however, normal atmospheric conditions
are preferred.
A variety of heating means can be useful to provide
the necessary hea-ting of the described heat develop~ble
photographic materials or thermographic materials according
to the invention. The heating means can be a simple hot
plate, iron, roller, infrared heating means or the like.
Although it is often undesirable, due to the lack
of control in preparation, the described photosensitive
silver halide can be prepared in situ in the described material
according to the invention. Such a method of preparation
of photographic silver halide in situ is described, ~or example,
in U.S. Patent 3,457,075 of Morgan et al, issued July 22, 1969.
- Due -to the limited solubility of some compounds, it
is often desirable to use organic solvents to aid in preparation
of the materials for coating to provide an element according
to the invention. Typical organic solvents which can be useful
in preparing a composition for coating as an antihalation
30- layer or filter layer according to the invention include
.
- - 26 -
,,

C,,~t,.~
tetrahydrofuran, methylene chlori.de, acetone and butanol.
~ixing of -the sol~ents with the described c'omponents accordlng
to the invention can be carried out using means known in the
photographic art.
Antihalation,materials and ~ilter materials according
to the in~ention can be useful with light sens:iti~e diazo-type
materials, vesicular imaging material.s or other non-sllver
imaging materials as desired.
The ~ollowing examples are included ~or a ~urther
understanding o~ the in~ention.
Example 1
The oxida-ti'~e dimer o:~ 2,L~,5-triphenylimidazole,
prepared according to the procedure described in the Jou~nal
of Organic Chemistry,.36, page,2265 (1971), (also known
as a lophine dimer) ~35.m'g) was dissolved in 1 gram o~
tetrahydrofuran. To the resulting composition ~as added ',
2 grams o~ a 20~ by weight acetone solution o~ the
polysul~onamide: poly(ethylene-co~l,~-cyclohexylenedimethylene-
l-methyl-2,~-benzenedisul~onamide). ~even milligrams o~
1?5-diphenyl-3-(para-methoxyphenyl)~ormazan dye was dissol~ed
in this solution, The resulting dye solution was coated on a "
poly(ethylene terephthalate) ~'ilm support at a 6 mil wet coa-ting
thickness with a doctor blade coating means. The resulting
coating was permitted to dry to pro~ide a heat bleachable
element according to the invention. The resulting element
bleached rapidly and comple-tely,upon heating by contacting
the element on a hot metal block at 150C ~or a ~ew seconds.
The general measure o~ the acti~ation enthalpy was made from
~ bleach rates at 90C and 112C and was approximately
29 kilocalories per mole. , ,
- - 27 -
_ _ _ _ _

Example 2
The procedure of Example 1 was repeatedusing a methylene chloride solvent in place of tetrahydro~uran.
The d~e-containing composition was coated at a 2 mil wet
coating thickness on a poly(ethylene terephthalate) f'ilm
support. The dye-containing composition was coated on the
support at the following coverage:
oxidative dimer of 2,4~5-trlphenyl- 4.8 mg/dm2
imidazole
triphenylformazan dye 1.1 mg/drn2
binder (a`s described in the21.5 mg/dm2
following Table I)
r~he following results were obtained with the
noted po~mers ss doscribed in Table I.
~ ' '
. .
.
- 28 -
, .
.

. .,
~13
m
O J
o
~O ~> 0~ r~l ' '
~. ~ o ~ .
~ 1~
C) ~ :
(V
O~
o
~1
.
~ ~ :
~ ~ ~ CO
.~: o O
~,
o o
td
~ . . . . ..
- o
:: H
1 , ',
.~ ~
.
. CO' O
3 ~ ~o
O ff: O ~i
~ U~
Q~
¢
~ O.
a) c~
' ' ~ ~ O
a)
. ' ~ ~` ~,~ O '
,~ ~ O ~ 15~ ,,
', ~0
~ O O O
C ~ 5 u~
~ ~1 1 ~1
" ~ ~
a~ . ~ :
O 0,!~ 0
'
- 29 -
., , ~
,
. .: . :

The elements were incubated at 38C at 50~
relative humidity. The results indicated a minimum loss of dye
density and no signi.ficant impai.rmen-t of bleaching even
after 3 weeks incubation. Incubated, preb]eached samples
also showed no color-return after 3 weeks a-t the described
incubation conditions.
Example 3
The procedure descr:ibed in Example 2 was repeated
using the described polyester binder with the concentration
of the components in the coating as f'ollows:
oxidative dimer of 2,4,5-triphenyl- 5.4 mg/dm2
imidazole
triphenylformazan dye 3.2 mg/dm
polyester binder (as described in 21.5 mg/dm
Example 2)~
~-toluenesulfonlc acid 1.1 mg/dm2
me coating was heated as described in Example 2.
No volatiles were observed to be released from the coating
containing the described acid upon heating as described at
160C for 10 seconds.
Example 1~
A tetrahydrofuran formulation was prepared similar
to that described in Example 2 with coatings containing:
triphenylformazan dye 1.1 mg/dm2
polysulfonamide binder 21.5 mg/dm
I'he mole ratios for the oxidative imidazole dimer
were varied between 0.5 moles of dimer per mole of dye and
2.75 moles of dimer per mole of dye in 0.25 mole increments.
me results were compared to unbleached coatings. The results
, , :
.... . .. . . . .. _ .
, :' ~ ' : ' ' ' , ~

.r~
indicated that an optimum level'for the par-ticular formulation
was about 1.6 moles o~` the described dimer per mole o~ dye.
This provided excellent bleaching,properties for the coating
when heated for 5 seconds at 160C. It also provided
excellent bleaching properties when the coating was heated
at 150C for 10 seconds. The bleach:ing properties
of the coati.ng were good at lL~0C when it was heated for
10 seconds but less desirable when the coating was heated
at 130C for 10 seconds.
Example 5
A tetrahydrofuran formulation similar to that
described in Example 2 was prepared containin~g the following: '
triphenylformazan dye 1.1 mg/dm2
oxidati~e imidazole dimer (as 3.1~ mg/dm2
- described in Example 2)
,A polysulfonamide-binder was mi~ed with the
formulation at concentrations from 50 to L~oO mg/ft2
(corresponding to 5.L~ to 43.1 mg/dm2) in varying increments.
, ' ' It was ~ound that after incubating the resulting
coatings at 38C and 50~ relative humidity for 4 ~eeks that
more dye was lost on incubation with lower polymer levels. '~
Upon incubation the polymér coverage of 37.7 mg/dm2 exhibited
less than 20~ dye loss in 4 weeks and about 10~ dye loss
' in 2,weeks. Ghanges in ~ormulation may provide dif~erent
stability correlations.
.
~xample 6
~ tetrahydrofuran formulation was prepared similar
to that described in Example 5 containing the following: '~
triphenylformazan dye 1.1 mg/dm
oxidati~e imidazole dimer 3.8 mg/dm2
polysulfonamide binder (as 32.3 mg/dm
described in Example 1)
- 31
.

tr~.,;3
The following acids at coverages of 2.5, 5, 10 and
20 mg/ft2 (corresponding to 0.2, o.46, 0 93 and 1.87 mg/dm2)
were also added to the formulation prLor to coating on a sup-
port as described in Exarnple 5:
~-toluenesulfonic acid
l-naphthoic acid
A~ter incubation, the results demonstrated that
low levels (5 mg/ft2) of l~naphthoic acid appeared to pro-
vide less dye loss on incubation, slightly -lncreased
processing rate, and did not affect the stain observed
after bleaching of the resulting coating. Higher levels
of this acid, or use or para-toluenesulfonic acid, produced
coatings with properties which were less desirable than a
coating which did not contain the incorporated acid.
~Z
A tetrahydrofuran formulation was prepared similar
to that described in Example 5 containing the following
components:
triphenylformazan dye 1.1 mg/dm2
oxidative imidazole dimer 5l4 mg/dm2
polymeric binder consisting of21.5 mg/dm2
copoly(maleimide-styrene)
(50:50 parts by weight)
(Lytron 820, a trademark of and
available ~rom Monsanto Company,
U.S.A.)
The formulation waB coated on a support and then
heated. The coating provided clear bleaching to a colorless
material with no visible evolution of volatile components.
32 -
i`
~ ~ " . , ' ~ , ,

Example 8
This lS a comparative example.
Using a tetrahydrofuran formulation similar
. to that described in Example 5, coatings were prepared
containing the following components:
triphenylformazan dye 1.1 mg/dm
o~idati~e imidazole d:imer (as 3.2 mg/dm2
described below)
poly6ulfonamide binder21.5 mg/dm2
(as described in Example 1)
Y'he following imidazole dimers were i.ncluded
individually in the above formulation:
2-~ortho-chlorophenyl)-4,5-
diphen~llmidazole dimer
2-(ortho-methoxyphenyl)-4~5-
diphenylimidazole dimer
The above formulation was tested with and without
~-toluènesulfonic acid as an addenda (at 5 mg/f-t2 corresponding
to 0.46 mg/dm2).
Upon heat processing of ~he resulting coating after
coating the formulation on a suitable support, minimal bleaching
was observed in the coating after heating at 200C for
30 seconds.
This indicated that the described imidazole dimers
are in the above formulation, too stable toward thermal
degradation to be optimally useful at the temperature and time
used.
xample 9
~ Certain of the oxidative imidazole dimers ha~e
llmited solubility in certain solvents. The solubility Or
certain imidazole dimers is limited to methylenechloride
formulations and tetrahydrofuran formulations.
- 33 -
~,

An.acetone .~ormulat;ion was prepared by mixing thefollowing components and coating on a transpalent
poly(e-thylene terephthalate) ~ilm support:
- triphenylformazan dye . l.1 mg/dm2
solubiliæed imidazole oxidative 4.0 mg/dm
dimer of:
N ~C6~I5
(H3C)2cH ~ N
6 5
polysulfonamide binder (as 32.3 mg/dm2
described in Example l)
After the above formulation was coated on a
film support~ the coating was permitted to dry and then
. .
heat processed by heating the element at 160C for lO seconds.
mis provided good bleaching of the coating.
The coating before bleaching was incubated
4 weeks at 38C and 50~ relative.humidity. I'his resulted :~
in a 37.5~ loss in dye density with no impairment of bleaching
abilit~ at 160C.
Example 10
Additi.onal imidazole dimers were also included
in a heat bleachable layer. These were solubilized imidazole
oxidative dimers of compounds within the following formula:
,, :
';
_ ' ' ' ,
, '' ' ,:
_ 31~ .
., . _ _ .. . ... _ , ..
, . ..
! ~

HN N
X Y
.
10 A Isopropyl H (Mono)
10 B H Isopropyl (Bis)
10 C Isopropyl Isopropyl ~Tris)
10 D Methyl H
Coatings were prepared using tetrahydro~uran as
a coating solvent at the following levels o~ components:
oxidative imidazole dimer 3.7 mg/dm
triphenyl~ormazan dye 0.93 mg/dm2
polymeric binder 28.0 mg/dm2
The polymeric binder was either maleic anhydride-
styrene copolymer or a polysul~onamide binder (poly(ethylene-
co-l,~-cyclohexylene-dimethylene-l-methyl-2,4-benzenedisul~on-
amide)). The coating was per~itted to dry to provide an ele-
ment according to the invention. me ~ormulation was c,oated ,
at a 2 mil wet coating thickness on a poly(ethylene terephth
alate) film support.
Good b~eaching properties o~ the resuIting element
~20 were observed when the element was heated at 160 for 10 secondswith both polymeric binders and with each of the described
imidazole dimers with a minimal stain seen at an absorption
of 400 nanometers.
Better incubation atability properties were observed
with the maleic anhydride-styrene copolymer as a binder.
- 35 -
., , ~,

Example 11
me procedure described in Example 10 was repeated
with Compound 10 B with the exception -that acetone was used
in place of tetra~ydrofuran. The dimer was found to have
excellent solubility in an acetone ~ormulation.
A coating containing this dimer demonstrated
excellent bleaching at 160C when heated for 10 seconds.
Example 12
m e described oxidative~ tris-subs-tituted, imidazole
.
dimer (Compound 10 C in Example 10) was also included ln a
~ormulation in a similar manner to that de,scribed in Example 10
using 0.9 mg/dm2 of' triphenylformazan dye and 28 mg/dm2 of the ,~
described polymer~c binder consisting o~ maleic anhydride-styrene
copolymer. Good bleaching properties were observed when the
resulting coating was heated f'or 10 seconds at 160C.
Good results we're also observed when the described
tris-substituted dimer (Compound 10 C) was coated at higher
leveIs.
Examples 13-16
The following dyes were evaluated:
OH HO
N=N ~ ~;
Dye A ;
C1
~ N=N C113
- OH
H ~ N/
Dye B
- ~,6 -
.
"

53 3
~o~
Dye C
S2NH2
=N OC2H5
~' ,~N
HO , N
'' [~ '~
Dye D
Method
Stock solution (A): In 7 grams acetone were dis-
solved 350 mg 2 phenyl-4~5-bis(p-isopropylphenyl)imidazole
dimer.
~;
~: .
(a) In 0,7 grams stock solution (A) were dissolved
6 mg Dye A (above). To this was added 1.4 grams of 15 weight
percent poly(vinyl butyral) (BUTVAR B~76, a trademark of and
available from the Monsanto Company, U.S.A.) in 1:1 acetone~2-
methoxyethanol. This solution was coated with a ~-mil doctor
blade on subbed poly(ethylene terephthalate) film support.
37 -

Example lL~
(a) was repeateA using lO mg of Dye B, above.
Example 15:
(a) was repeated using 9 mg D~re C, above. (A few
drops of methyl ethyl ketone were added to help dissolve the d~e).
Example 16
,
(a) was repea-ted using 12 mg Dye D, abo~e.
rme resulting fi.lms were hea-ted, face up~ on a 150C
block and the time irl seconds to bleach was noted. Diffuse
densities were read beforb and after heat bleaching, r~he
results are given in following Table Il.
.. ' ' ~
.
:
~ ' '` . ' ~
':
.
.
3~ ,
.
.

~ ,
~rl _~
u~
~ a) a) a
~ m m ~ m
a)
C) N N r-l ~1
a) o o o o
pl , ' , .
' ~ . .
~rl -~
E-l ~
ul
, ~ N ~--1 H
H r-l
r-l
.
... ,
a
C~ r~
~ a~ o
h O O O O
' : '
Fl ¢ a~ v ~
. ' .~ , ,
a
L~ ~D
~ . ' '
,
,''
-- 39 _
. . .
.

~ le for~azan dyes and their preparation are known
in~the art. The formazan clyes can be prepared using procedures
known in the art, such as described in Chemical Reviews, 1955,
. beginning at page 356.
The coverages and proportions of the various
components which comprise the described dye-biimidazole
combinatiQn of the present invention can vary o~er wide ranges
depending upon such factors as the particular use, location
in the element of the antihalation or fllter component, the
'10 desired degree of absorption, pYocessing temperatures and
the like. For example, in some thermographic uses, the
concentration of dye is suff`icient to provide an optical
density of at least about 0.05. To pro~ide discrimination,
the hexaarylbiimidazole need be present in an amount suff'icient
to reduce the density of the dye by at least an amount that
provides a desired image when the element is heated above
about 70C. F'or antihalation purposes on the other hand,
it is desirable that the concentration of the dye'be sufficient
to provide an optical density of at least about'0.2 such as
about 0.3 to about o.8. The hexaarylbiimidazole must be
present~in at least sufficient concentration to provide at least
40~ bleaching of the described dye. With formazan dyes,
for example, a useful concentration is within the range of 0.2
to 10 moles of the hexaarylbiimidazole to 1 mole of formazan dye.
-Typically, an excess of the hexaarylbiimidazole compound
insures the desired degree of reaction with the described
dye in the elements in which the dye is used for antihalation
purposes.
,

o
tno~q~ ,
The preferred~ratio O:r hexaarylbiimidazole compound to dye
'a~'~'' is within the range o~ about o.4 to about 3.0 with an especially
~useful ratio being about 1.0 to 1.5. The exact mechanism
by which the described dye and dye-containing layer change
' from colored to colorless is not complete:Ly understood. '~lowever,
' it is believed that the hexaarylbiimidazole compound upon
heating forms radicals which react with the dye in a manner
which changes the dye structure from colored to a ].ess
highly colored material. 'l'his reaction is believed to
significantly contribute to the surprising stability of the
colorless layer after heating.
The elements according to the invcntiorl can c'ontai.n
.,
various colloids and polymers alone or in combination as
vehicles, bindin~ agents-and in various layers. Suitable
materials as described~are hydrophilic materials or'hydrophobic
;
' ~ ' materiaIs. The colloids ancl polymers are transparent or
'~- translucent and include those materiàls which do not adversely
af~ect the reaction which changes the dye from colored to
colorless and which'can withstand the processing temperatures
' 20 employed. These colloids and polymers include, for'example,
- -proteins such as gelatin~ gelatin derivatives, cellulose
derivatives, polysaccharides such as dex-tran and the like;
and synthetic polymeric substances such as water soluble
polyvinyl compounds like poly(vinyl pyrrolidone)~ acxylamide
polymers and the like. Other synthetic polymeric compounds
which can be useful include dispers~ed vinyl compounds such as
i~ la~ex form. r3ffective polymers lnclude hi~ll molecular
weight materials, polymers and resins which are compatible
_ with the imaging materials of the element. When a formazan
dye is used with a hexaarylbiimidazole for antihaiation purposes,
a useful binder'is a polysulfonamide. One useful
' '' ' ' - 12 - ' " '
.
; " , , ' ' ' . . ' '
i. . ::

polysulfonamide binder is a poly(ethylene-co-1~4 cyclohexylene-
dimethylene-l-methyl-2,4-benzene disulfonamide) binder~
Combinations of the described colloids and polymers can also
be useful if desired. Als~, water ~nsoluble polymers, ~uch as
poly(vinyl butyral)~ such as BUTVAR B-76, a trademark product
available from the Monsanto Company, U S.A., ~nd latexes which
are compatible with the antihalation or filter compounds are
useful.
The antihalation layer as described can be use~ul
in a variety of photographic elements. Useful photographic
elements include those which are designed to provide an image
from photographic silver halide~ such as color images, or
elements designed for non-silver imaging. Photographic
elements which are designed for microimaging are especially
useful with-the antihalation materials according to ~he
invention.
The described combination of the hexaarylbiimidazole
compound and dye, especially the formazan dyeg can be in any
suitable location in the imaging element which provides the
desired bleaching of the dye upon heatingO Other of the
described components of the imaging element according to the
invention can be any suitable location in the element which
provides the desired image. For example, if desired, one or more ;~
components of the imaging element according to the in~ention
can be in one or more layers o~ the element. In some cases~
it can be desirable to include certain percentaees of the
described reducing agents, image stabilizer or stabiliæer
precursors, dyes an~/or other addenda in a protective layer
over the heat developable element. In some cases this can
reduce migration Or certain addenda between the layers of the
descri~ed elemeht.
'~6'~

It is necessary that the i,mage-formi.ng components
in the imaging material acco:rding to the invention 'be in
reactive associa~ion with each other in order to provide the
. desired image. 'It is also necessary that the described dye
- and hexaar~lbiimidazole compound be in reacti~e association
with one another -to provide the desired heat bleaching in
the imaging element. The term "in reactive association"
as emplo~ed herein is intended to mean -that the described
materials are in a location with respect to each other which
enables the desired processing and heat bleaching and provides a
more useful developed image. The term is also employed herein
to mean that the hexaarylbiimidazole compound and the dye
are in a location with respect to each other which enables the
desired change of the dye from colored to colorless upon heating
as described. For example,, one o~ the components can be in
one layer o~ an imaging element and other components in one or
more other lavers with the provision that the~ are in reactive
association.
The heat developable photographic materials
according to the invention comprise a photosensitive component
which can be a silver photosensitive component or non-sil~er
photosensitive component, When a silver photosensitive
component is used, photosensitive silver halide is
especiall~ use~ul due to its degree o~ photosensitivit~ '
compared to other photographic components~ A typical
concentration of'photosensitive silver halide in a heat
developable photographic element according to the invention is
within the range of about 1 x 10 4 to about 10 1 moles of
,_ photosensitive sil~er halide per square meter of support.
Other photographic materials can be useful in the described
elements according to the invention if desired. Preferred
.
!,

photographic silver halides are silver chloride, silver'bromide,
silver bromoiodide, silver chlorobromoiodide or mixtures thereof.
For purposes of the invention, silver iodide is also considered
- to be a useful photographic silver halide. ~ery fine grain
photographic silver halide is useful although coarse or
fine grain photographic silver halide can be used if desired.
The photographic silver halide can be prepared by any of the
procedures known ~n the photographic art, especially those
procedures'which involve the preparation of photographic
silver halide gelatino emulsions. 'Useful procedures and
forms of photographlc silver halide ~or purposes of the
invention are described, for example, in the Product
icensin~_Index, Volume 92, December 1971, publication 9232
on page 107, published b~v Industrial Opportunities Ltd.,
Homewell, Havant,Hampshire, PO9 lEF~ U~. rme silver halide
compositions described in ResesIch Disclosure, Vol. 148,
August 1976, Item 14879 of ~osenfeld and Research Disclosure,
September 1974, pages ~3-45 are'further examples of useful
silver halide materials. The photographic silver halide as
described can be unwashed or washed, can be chemically
sensitized using chemical sensitization procedures ~nown in
the art, can be protected against'the production of fog and
stabilized against the loss of sensitivit~ during keeping as
described in the above Product Licensing Index publication.
A variet~ of non-silver photosensitive components' i '
can be useful with the described photographic elements. r~hese
can be, for instance, photosensitive diazo imaging materials,
imaging materials based o~ photoreductants, photosensitive dyes
_ and the like. The term "photoreductant" or "photoreductants"
- 15 -
, .~,; :
.. . . , .......................... . ~ .
.: , . . , . , :

as used herein is intended to mean a material capable of
molecular photolysis or photoinduced rearrangement to generate
a reducing agent capable of reducing an imaging agent~ or a
reducing agent precursor which can be c~nverted to ~uch a
reducing agent. Useful non-siIver pho~osensitive components
are described, for example, in Research Dlsc1osure, October 1974,
Item 12617, pages 12-30. The non-silver photosensitive
components can include combinations o~ such components) 1~
desired. An example of a non-silver photosensitive material,
comprises a quinone photoreductant, such as 2-isopropoxy-1,4-
naphthoquinone, with a cobalt amine complex3 such as
hexa-amine cobalt (III) acetate, as described in the above
Research Disclosure.
Especially useful photosensitive materials are
those designed for microimaging purposes.
m e described heat developable photographic material6
can comprise a variety of reducing agents, especially organic
reducing agents which are typically photogr~phic silver halide
developing agents. m ese reducing agents can be use~ul i~
combination. ~educing agents which are especially use~ul are
~ilver halide developing agents including poIyhydr~xybenzenes,
such as hydroquinone, alkyl-substituted hydroquinones, including
tertiary-butyl hydroquinone, me~hyl hydroquinone, 2,5-
dimethyl h~droquinone, and 2,6-dimethyl hydroquinone; catechol
and pyrogallol developing agents; chloro-substituted
hydroquinone such as chlorohydroquinone or dichlorohydroqulnone;
alkoxy-substituted hydroquinones ~uch as methoxy hydroquin~ne
or ethoxy hydroquinone; aminvphenol reducing agents such as
2,4-diaminophenols and methylaminophenols; ascorbic acid
. . ~, .
. ' :
..
.

developing agents such as ascorbic acid, ascorbic acid ketals
and ascorbic acid derivatives; h~droxylamine reducing agents;
3-pyrazolidone reducing agents such as 1-phenyl-3-pyrazolidone
and 4-methyl-4-hydroxymethyl-1-phenyl-3-pyrazolidone, reduc-tone
reducing agents, such as 2-hydroxy-5-methyl-3-piperidino~2-
c~clopentanone; gallic acid ester reducing agents such as
methyl gallate, sul~onamidophenol reducing agents such as the
suIfonamidophenol reducing agents described in Research Disclosure
January 1973~ pages 16-21, published by Indus-trial Opportunities
Ltd., Homewell, Havant~Hampshire, ~09 lEF3 UK; phenylenediamine
silver halide developing agents such as paraphenylenediamine
and the like. Especia:l]y useful heat developable photographic
materials can contain combinations o~ reducing agents as
described.
The optimum concentration o~ reducing agent can be
determined based upon such factors as the desired image,
other components in the heat developable material, processing
conditlons and the like.
me term "reducing agent" as employed herein is
intended to include reducing agent precursors as well as
reducing agents. That is, the reducing agen-t precursors
are intended to include compounds which ~orm a reducing
agent upon heating or exposure to some other condition
at the desired time.
~ he imaging materials according to the inven-tion
can contain~an image toner or toning agent in order to
provide a more neutral or black tone image upon processing.
The optimum image toner or toning agent will depend upon
- 17 -
~ l*~ ~ '~

such factors as the parti.cular imaging material~ the
desired image, par-ticular processing conditions and the like.
In some cases certain image toning agents or toners pro~ide
much better results with certain imaging materials than with
others. Com~inations of toning agents or toners can be useful
if desired.
The optimum concentration of toning agent or toning
agent combination will depend upon such fac-tors as the
particular imaging material, processing conditions, desired
image and the like.
It is often useful to include a melt-forming compound
or melt former in the imaging materials according to the
invention such as in the imaging la~ers and in the
antihalation layer or filter layer, as described. Combinations
of melt-forming compounds or melt-formers can also be useful
if desired. The term "melt-forming compound" or "melt former"
as employed herein is intended to mean a compo~nd which upon
heating to the described processing temperature provides an
improved reaction medium, typically a molten medium, whereln
the described reaction combination can pro~ide a better image.
The exact nature of the reaction medium at processing temperatures
- described is not fully understood; however, it is belie~ed that
at reaction temperatures a melt occurs which permits the reaction
components to better interact. Useful melt~forming compounds
are typica~ly separate components from the reaction combination,
although the reaction combination can enter into the melt
formation. Typically useful melt-forming compounds are
amides, imides, cyclic ureas and triazoles which are compatible
- ~ 18 -
.'' , '
' '
. i ~
.: , ~ : , . ~ . , .
.

with other of the components of the ma-terials of the
in~ention. Useful melt-forming compounds or melt formers are
described, ~or example, in Research Disclosure, Vol. 150,
October 1976, Item 15049 of LaRossa and Boettcher, published
by Industr:Lal Opportunities Ltd., Eomewell, Havan~ Hampshire,
PO9 l.EF, UK. As described, the antihalation or filter layers
of the invention can comprise a mel-t-forming compound if
desired.`
A range of concentration of melt-forming compound
or melt-forming compound combina-tion is useful i~ the hea-t
developable photographic materials described. I'he optimum
concentration of melt-formi.ng compound will depend upon
such factors as the particular imaging material, desired
image, processing conditions and the like.
Spectral sensitizing dyes or dye combinations are
useful in the described imaging elements and compositions
of the invention to confer additional sensitivity to the
elements and compositions. Useful sensitizing dyes are
described, for example, in the Product Lic_n ~ x,
Volume 92, December 1971, publication 9232, published by
Industrial Opportunities Ltd., Homewell, Havant,Hampshire PO9 lEF,
UK.
The imaging materials according to the invention can
also have a range of pAg. The pAg can be measured using
conventiona~ calomel and Ag-AgCl electrodes, connected to
an Orion digital p~ meter. me typical pAg in a heat
developable photographic material according to the invention
is within the range of about 2 -to about 13. The optimum pAg
- will depend upon the particular imaging material, the
desired image, processing conditions and the like.
,

~ 3
The imag~ng materials according to the invention
typicall~ have a pH range'which is on the acid side o~ neu-tral,
that is a pH of less than about 7. Typically useful pH f'or a
heat developable photographic material according to the
- invention is within the range of about 2 to a'bout 6, preferabl~
within the range o~ about 3.5 to abou-t ~Ø The combination
of the described biimidazole and dye .is also useful on the acid
side of neutral, that is a pII of less than about 7.
It is often desirable to have a stabilizer or
stabilizer precursor in'the described imaging materlals
according to the inven'tion ~o impr'ove pos~-processing
image stability. In some cases the heat developable photographic
materials may be sufficiently stable in the absence of a separate
stabilizer or s-tabilizer precursor. However, in man~r cases
in which photographic silver halide is used as the
photosensitive material it can be desirable to stabilize
the silver halide after processing in order to avoid
undesirable post-processing printout. A variety of stabilizer
,
or stabilizer precursors is useful in a hea~ developabLe
photographic material as described. The stabilizers or
stabilizer precursors can be used alone or in combination
if desired. Typically useful s~abilizers or stabilizer
precursors are sulfur-containing compounds which form a
stable silver mercaptide upon heating in the heat developable
photographic material. Useful stabilizers or stabilizer
precursors include, for instance, those described in
Belgian Patent 76~071 issued July 30, 1971,
0 --
", ' ' ' : ~ '

Pho-to:lytically activated po:Lyhalogenated orgtln:lc compounds'
can be usefu:L if desired. Such photolyticalLy ac'tivated
polyhalogenated organlc compounds are described, for example,
in U.S. Patent 3,871~,946 of Costa et al, issued April 1, 1975
and U.S. Patent 3,707,377 of Tiers et al, issued December 28, 1972.
- 'A range of concentration of stabilizer or stabilizer
precursor or a combination of these compounds can be useful
in the described imaging materials. An optimurn concentration
of' stabilizer or-stabilizer precursor or combination of these
compounds will depend upon such factors as the particular
imaging ma-terial, processing conditions, desired stability
and the like.
A development activator, also known as an alka]i-release
agent, base-release agent or an activator precursor can be
useful in the described~imaging materials of the invention.
A development activator, as described her'ein, is intended -to
' mean an agent'or a compound which aids the developing agent
at processing temperatures to develop a la-tent ima~e in the
imaging material. Useful development activators or activator
precursors are described, for example, in Belgian Patent 709,967
published February 29~ 1968, and Research Disclosure,
Volume 155, March 1977, Item 15567, published by Industrial '
Opportunlties Ltd., Homewell, Havant,Hampshire, P09 lEF, UK.
Examples of usef'ul activator precursors include guanidinium
compounds such as guanidinium trichloroacetat'e, diguanid-inium
glutarate, succinate, malonate and the like; quaternary
ammonium malonates; amino acids, such as 6-aminocaproic
acid and glycine; and 2-carboxycarboxamide activator
recursors
p
3~ ' It is usef`ul in some cases to have an overcoat
layer on the imaging element such as on the imaging layer and
the'antihalation or filter layer according to the invention
, ~
- 21 -

to reduce fingerprill'ting and ab~asion marks and provide okher
advantages. I~e overc'oat layer can be one or more of the
described polymers which are also useful as binders. However,
' other polymeric materials which are compatible with the imaging
- layer of the element of the inveMtion and which can tolerate
the processing temperatures employed can be useful. Such other
binders' or polymerlc materials include, for instance, cellulose
acetate and polyviny] 'chloride. Combinations of polymer'ic
materials can be ~sefu]. for overcoat purposes if desired.
' The imaging materials according to the invention,
especially the photographic silver halide imaging materials,
can contain other addenda such as development modifiers
that function as speed-increasing compounds, hardeners,
plasticizers and lubricants, coating aids, brighteners,
antlstati'c materials or layers, antifoggants and the like.
mese are described, for example, in the Product Licensing
Index, Volume 92, December 1971, publlcation 9232,
pages 107~110, referred to above.
The imaging elemen-ts according to the invention
can comprise a ~ariety of supports which can tolerate the
processing temperatures employed according to the invention.
Typical supports include cellulose ester film, poly(vinyl
acetal) fil~, poly(ethylene ~erephthalate) f'ilm, polycarbonate
film and polyester film supports as described in U.S
Patent 3,634,o89 of Hamb, issued July 11, 1972 and U.S.
Patent 3,725,070 of Hamb et al, issued April 3, 1973.
Related film and resinous support materials, as well as glass, paper,
metal and the like supports'which can w1thstand the processing '''
~ temperatures described and which can be useful with the
described filter and antihalation layers are also ~seful.
T~pically a flexible film support is most useful.
. - 22 -
. _ . _ . : ,, . . . . .. __ __ _...... . . _ . . .. __.. ___ _ _ . . .. .. , .. ~ .. _ _ _ _ "
.. . . . . . . .

The antihalation materials comprising the
combination of the described clye, especi.ally the f'ormazan
dye, with the hexaarylbiimidazole compound can be present
in a transparent support if desired, such as in a tra.nsparent
film support. ~or example, cellulose triacetate and polyester
film supports which can be use~ul ~or a heat de~elopable
photographic element can contain the described
combination of the hexaarylbiimidazole compound wlth a dye,
especially a for.mazan dye.
. The antihalation and ~ilter components accord:ing
to the in~rention as well as -the o.ther compositions described
can be coated on a suitable support b~ various coating
procedures k~own in the photographic art including dip coating,
airknife. coating, curtain coating or extrusion coating using
' hoppers, such as described in U.S. Patent 2,681,294 of ~eguin,
issued June 15, 195l~.' If desired, two or more layers can be
coated simultaneously such as described in U.S. Patent 2,761~791
of'Russell, issued September 4, 1956 and British Patent o37,095
published June 9, 1960.
. While a variety of components can be useful in a
described antihalation layer according to the in~rention,
it is often desirable -to ha~re a combination that becomes
at least 90~ colorless within less than about 30 seconds upon '
heating the element to a temperature.of at least about 130C.
This combination'can be useful in a photothermographic
material as described. It can also be useful in a ~ .
thermographic material.
In some cases it is useful to have a small
concentration, typically up to about 6 milligrams, of
l-naphthoic acid per square foot of support in the combination
con;taining the biimidazole compound. The presence of the
- 23 -

l-naphthoic acid pro~ides the advantage of :reducing undesired
release of volatile ma-terials from the comb:ination containing
the biimidazole compound. Other acids that are useful inc:Lude
2-naphthoic and benzoic acids. Selection of a suitable
- binder can influence the desirability of the addition of a
separate acid compound.
An especiall~ useful embocliment bf the invention
is a photographic element comprising (a) a support having
thereon (b) at least one silver halide photosenslti~e
layer, and (c) at least one antihalation layer comprising,
in reactive association, (i) at least one compound represented
by the formula (I)~ as described, with (ii) at least one
formazan antihalation dye, and (iii) a polymeric binder
comprising a maleic anhydride-st~rene copolymer, wherein the
antihalation layer becomes at least about 90~ colorless within
about 30 seconds upon heating to a temperature of at least
about 120C
A yarie-ty of imagewise éxposure means are useful
for imaging according to ~he invention. I~e elements according
to the inventio~ are typically sensitive to the ultraviolet
and blue regions of the spectrum and exposure means which
provide this radiation are preferred. Typically, however,
if a spectral sensi-tizing dye is employed in the described
photographic materials, exposure means using other ranges of ~ -
the electromagnetic spectrum can be useful. T~pically a
photosensitive element according to the invention is exposed
imagewise wl~h ~ vls:L~le ll~t SOU:I.`Ce sU('h lS '1 tll~I(`;l` ~ell
to provide a developable image, although other sources o~
_ radiation are useful such as lasers, electron beams and the
like. I~ the case of thermographic elements according to the
:,
- - 24 _

The ~ollowing oxidati~e triar~limidazole
dimers were tested. A11 dimers were tested in hand coatings
with triphen~lformazan d~e in a pol~neric binder. The compounds
were oxidative dimers of:
R3
H
~ ,
R2 ~2
wherein R2 and R3 were as defined in following Table IIIo
All substituents are in~the para position unless otherwise
indicated in Table IIIo
,

3~3
,
rl rl rl
~1 ~o ~ ~1 0 0 0 0 o ~1 o O O O O
~r~~3 m m ~ m
r-l r~ ~ m P~ m P~ P~ P ~ ~ m r, P~ m m
O ~d ~rl ~ d r~ rl ~ ~ ~1 ~ ~
æ ~ ~ ~ c~ cg ~, c~ ~ ~ O ~ ~, ,
O
.
H~ W W W W a 0 5 ,q S X ,
~ ~rl rl 1 ~ rl (1) ~rl
i I
5 ~ X II' ~ ~ 5
01 01 ~rl ~ ~ri ~ 0 I ~ l ~1 0 1
." . ~: ~
rl ri r
¦ ~ co ~ p~ O ~d p, O ~I N 0 ::1 ~ O ~ Pl ~~ ) ~1
,:
~, , .
- 41 -
. i . . ,.~ .

Metal chelates of the described formazan compounds
are also useful for the purposes described.
Example 32 - Bleaching of a Complexed Formazan Dye
In 0.4 g of warm 2-methoxyethanol was dissolved 2 mg
Or cupric acetate monohydrate and 6 mg of triphenylformazan
to give a dark purple solution. To this solution was added
1.4 g of a 15~ by weight solution of poly(vinyl butyral)
(BUTVAR B-76) in 1:1 parts by weight acetone/2-methoxyethano1
and a solution of 50 mg of the oxidative bis isopropyl
substituted triphenylimidazole dimer, as described, in
0.3 g of 1,2-dichloroethane. The resulting solution was
coated at a 4 mil wet coating thickness on a poly(ethylene
terephthalate) film support containing a subbing layer.
-The resulting-film had a grey-purple color. A sample of this
film having a neutral diffuse density of o.36 was heated
foY 5 seconds face-up on a 140C hot metal block. This caused
bléaching of the coating. The neutral diffuse density of
the heated film was 0.09.
'
Example 33
A coating was prepared containing the following
materials with a 2 mil doctor blade:
300 mg/ft2 BUTVAR B-76 (poly(vinyl butyral))
10 mg/ft2 Dye 33A
100 mg/ft Bis isopropyl substituted oxidative
triphenylimidazole dimer, as described3
employing acetone as the solvent.
Dye 33A is represented by the following structure:
~2

(,OEI3)2
H H ~ < CH3
CH2CH20H Br~
Dye 33A (.Polymethine Dye)
Application of heat to this coating (160C for 10 seconds)
resulted in a bleaching of the dye from a density (at ~max)
o~ 0.360 to 0.105 after bleaching (71~ change).
Example 3~
The procedure described in Example 33 was repeated
with the exception that Dye 34B was used in place of Dye 33A.
Dye 3~B is reprèsented by the following structure:
H03S ~ N - C' C - N ~ S03H
. N /C=CH-CH=CH-C~ //N
CH 3
Dye 34B (Oxanol dye)
Application of heat to this coating (160C for 10 seconds)
resulted in a bleaching (at Amax = 540~ of 0.42 to a density
after bleaching of 0.165 (a 61% density decrease). ~:
Example 35 - Use_of Melt Formers
A series o~ low melting solids (i.e. melt formers~
were added at 100 mg/ft2 (~11 mgjdm2) to the following
_ formulation: ~.
.
- 43 -

mg/ft
Triphenyl~ormazan 10 1.1
Bis isopropyl-substituted 50 5.4
triphenylimidazole d~mer,
as described
LYTRON 820 (a trademark of and 300 33
availa~le from the Monsanto
Company, U.S.A.) (Purlfie(l
Monsanto copoly(maleimide/
^styrene) (50:50)
The resulting composition was coated at a 2-mil wet coatlng
thickness from acetone solution onto a poly(ethylene
terephthalate) film support. A melt ~ormer was added
to the composition be~ore coating. A~ter drying the
coatlng, it was heated ~or 5 seconds at 130C. me results
were as follows~
130C - 5 sec.
Melt Former ~ Process
None (Control) ---Minimal Bleach
-20 Methanesulfonamide 91-93 Slight Bleach
Methylurea9~ 101 Good Bleach
Resorcinollog-llo Sli~ht Bleach
N-Methylbenzamide 79-82 ~ood Bleach
Methylurea- and N-methylbenzamide-containing coatings c-an
also be processed for 15 seconds at 120C to bleach the
described dye.
;:
Coatings were prepared at the same levels as in
Example 35, but employing poly(vinyl butyral) (BUTVAR B-76,
a trademark of and available from the Monsanto Company~
U.S.A.) instead o~ LYTRON 820. Processing at a hot block
~or following times and temperatures produced bleaching of
- the dye:
, ~,
.: ' ' ' .'" ' ` ~ '', ' ', ' ', '', , ~

~C. )
15Q 3
11~0 3
130 5
120 10
Examples 37~47
A series of pol~mers was tested in a compositlon
as follows: .
~ ~, . .
Polymer (see list following) 300 33
Triphenylformazan 10. 1.1
Bis isopropyl substituted 50 5.4
triphenylim~idazole dimer,
as described
,
In each instance the coating was heated ~or 10 seconds at
130C. The results were as follows:
' ~ ~
~ .
,
'
.
;;
,
,
~,
.; ~ .: ;.;.: . . ~;
.. , . ~ ,

U .
o , ~ ~i
~i .ri , (I)
rl C.) a~ r-¦ ~1 1
r l ~ m
r-j ~rl
bD~ LO Lf~ L~ O g r^l
~1~ V
~ ~ Xq ~
r-i b~. (D ~1 ~ri ~ ~i r-i
r i ~C I ,S:~ h O ~ ~ri
o ~ 0S-l--~ ~r_
r-lc3 0 .~j (¦) O C)~~ ¢ ~ ¢
--~ h,~ 4 r~ Q~ ~ h o
r-ih a) ~h ~ ha) ~rl (I)Ul hu~
r~ Q~ ~
Qc) s ~ O ~ ~ ri ~ s p
h a~~ cs 5~ H ~U~ r-i O O O
O ~ X ~ ~ U~ ~ Q~ rlr-l r-i
h ~ r~ ~ r~ --! r-i ~O r i v ~ v
O ~ cr i ~r
ri~ri r~rl~ t~ , r-i ~ri ri Q3~ Q~ ~ c3 ~ ¢
vi Q) vi ~i ~ O v~ cq a)~ 1) rh $ r-~ ri r~.r~
h N ~ 3 0 ~;
o ch~h ~ a) ¢ h~~ri ,5~) V
Q~ V C~ ~ Q~ ~ r I~nr-i m
Q ~ ~5V h
h C.~ P~u~h hl~ h o h h c~~ o r-i o ~ ~ o
Vi ~ vi (!~ r~ ~r I V vi vi ~~ r i ~; r-i ~ P~ ~ ~
~Oj
a~
i J ~ o
.

-
~xam~les 48-50 ~comparative examples)
The f'ollowing dyes were tested in a f'ormulation
similar to that described in ~xample 33 in place of' the
- Dye 33A. In each instance bleaching of' the dye was not
- satis~actory.
Example 48 (comparative example)
CH-CH=C \ 1 2 5
C2~I5
Example 49 (comparati~e example)
CH-CH=CH ~ .
C2H5 I~
Example 50 (compara-tive example)
N ~ ~ - C=S
C H
' .
_ 47
,

The :invention has been descrlbed in detall with
particular reference to preferred embodiments thereof, but
it will be understood that ~ariations and modifications can
. be effected withln the spixit and scope of the Lnvention.
,
,,
~ .~
,
' ' . , - ' ' :~
." ' ,' . ~
,.
-
~ - 48 - -
.