CA1116003A - Heat sensitive materials including a hexaarylbiimidazole dimer and an antihalation or filter dye - Google Patents

Abstract

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.

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

- 2 -,., ~

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 _ ~ ~ ..~.

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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.

-- .

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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 ~''' ' ' 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~

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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.

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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 .

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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. , , _ _ _ _ _ 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.
~ ' ' . .
.

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. ., ~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 ' ., , ~

, . .: . :

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 , , :

.... . .. . . . .. _ .

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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) .

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.

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~ ~ " . , ' ~ , , 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.

~, 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

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.

., , ~, 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 ;

~ N=N C113 - OH
H ~ N/

Dye B
- ~,6 -.
"

~o~

Dye C

=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.
~;

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(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.

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"

, .~,; :
.. . . , .......................... . ~ .
.: , . . , . , :

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 ~ 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, ", ' ' ' : ~ ' 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 , ~

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 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:

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 ,:

~, , .

. 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

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: ~.
.

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. ) 11~0 3 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 - -.

Claims

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 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 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:

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:

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.

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.

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:

wherein R and R' are individually selected from alkyl containing 1 to 4 carbon atoms and hydrogen.

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:

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-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.

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:

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 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.

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:

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 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.