CA1154996A - Light sensitive, thermally developable imaging system containing a bleachable or leuco dye, nitrate salt and diazonium salt - Google Patents

Abstract

LIGHT SENSITIVE, THERMALLY DEVELOPABLE IMAGING SYSTEM

Abstract The cost of conventional silver halide imaging technology has increased dramatically with the rising cost of silver. It would therefore be desirable to remove the silver from such imaging materials. Many replacement systems for silver tend to be complex without providing equivalent sensitometric results to silver halide systems.
A novel imaging system comprising (1) a polymeric binder resin, (2) a bleachable dye or leuco dye, (3) a nitrate salt, and (4) a light sensitive diazonium salt.

Description

49~6 ~ield of the Invention The present invention relates to light sensitive imaging systems. Mor0 particularly the invention relates to light sensitive, thermally developable diazonium salt imaging systems.
Summary of the Invention The present invention relates to an imaging system comprising 1) a polymeric binder resin, 2) any bleachable dye or a leuco dye, 3) a nitrate salt,and 4) a light sensitiv0 diazonium salt. In addition to these active ingredients, a material which supplies hydrogen ion, such as an acidic material, and in par-ticular an acid, is a desirable ingredient. Both positive and negative acting systems may be produced. After exposing the system to light, the application of heat will develop the image by bleaching the dye or oxidizing the leuco dye morerapidly in either the exposed or unexposed region. The presence of the acidic ~material accelerates the decolarization, or colorizing phenomenon.
Thus, this invention provides an imageable composition comprising a) a polymeric binder; b) a bleachable dye or a leuco dye, c) a non-reactive nitrate salt, d) a photosensitive diazonium salt and e) an acid, said nitrate salt in said imageable composition being capable of liberating }~03, N0, N02 or N204 in oxidiz-ing amounts when said composition is heated to no more than 200C for 60 seconds.
~hen a leuco dye is used in place of a dye, the leuco dye is oxidized to form a colored dye upon the application of heat. A positive acting system or negative acting sys~em will result because of the differential rate of oxidationoccurring in exposed and unexposed regions.
Detailed Description of the Invention There are a minimum of four components to the imageable systems of the present inventionJ and five components to the preferred constructions. The four required ingredients are 1) a bleachable dye or a leuco dye, 2) a nitrate salt, 3) a light sensitive diazonium salt, and 4) a polymeric resin. An acidic mater-ial constitutes the preferred fifth ingredient.
$

~1~4~6 The Blnder Any natural or s~nthetic polymeric binder may be used in the practice of the present invention. The pH of the resin has been ~ound to a~fect only the speed of the decolorizing or colorizing effect. If the speed is not important, any resin may be used. Organic polymeric resins, preferably thermoplastic resi~s (although thermoset resins may be used), are generally pre~erred.
Where speed is more important, either the more acidic resins should be used or an acid should be added to the system to reduce the pH and increase the rate of decolorizing or colorizing ti.e., leuco dye oxidizing).
Such resins as polyvinyl acetals, polyesters, polyvinyl resins, polyvinylpyrolidone, polyesters, polycarbonates, polyamides~ polyvinyl butyral, polyacrylate~, cellulose esters~ copolymers and blends of these classes of re~ins, and others have been used with particular successO
Natural polymeric materials such as gelatin and gum arabic may also be used. Where the proportions and activities of dyes and nitrate salt require a particular developing ~ime and temperature, the resin should be able to withstand those conditions. Generally it is pre~erred that the polymer not decompose or lose its structural integrity at ; 200F (93C) for 30 seconds and most preferred that it not 25 decompose or lose its struc~ural integrity at 260F
(127C) for 30 seconds.
Beyond these minimal re~uirements, there is no criticality in the selection of a binder. In fact, even transparency and translucency are not required, although 30 they are desirable. Where, for example, the polymer i~
itself an opaque white/ the light struck and thermally treated area in decolorizable sys ems will become white and the non-treated areas will remain the color of the dyeO
The binder serves a number of additionally important purposes in the constructions of the pre~ent invention. The imageable materials are protected from _ 3 _ ~5~9.~

ambient conditions such as moisture. The consistency of the coating and its image quality are improved. The durability of the final image is also significantly improved. The binder should be present as at least 25~ by weight of ingredients in the ;Layer, more preferably AS 50%
by weight and most preEerably as at least 70% by weight of dry in~redients (i.e., excluding solvents in the layer).

The Nitrate Salt Nitrate salts are themselves well known. It may be supplied as various compound Eorms, but are pre~erably provided as a metal salt, and most preferably provided as a hydrated metal salt. Other ions which are ordinarily good oxidizing ions such as nitrite, chlorate, iodate, perchlorate, periodate, and persulfate do not provide comparable results. Extremely active oxidizing agent~, such as iodate, even used in relatively smaller proportions to prevent complete and immediate oxidation or decolori~ation of dyes, do not perform nearly as well as nitrate ion compositions. The performance of nitrate is so far superior to any other ion that i~ is apparently unique in the practice of the present invention. While some of the better oxidizing ions other than nitrate can produce a maximum density ~DmaX) in the image of about 0.~0 and a minimum density (Dmin~ of 0.25 in their best construction, the better constructions with nitrate ions ; can have a DmaX in excess of 1.0 and a Dmin below 0.20 or even 0.10.
Mos~ means of supplying the nitrate ion into the composition is satisfactory. Metal salts, acidR, acid salts and other means o~ supplying the ion are useful.
For example, nitrates of zinc, cadmium, potassium, calcium, zirconyl, nickel, aluminum, chromium, iron, ; copper, tin, magnesium, lead, silver and cobalt~ ammonium nitrate, and ceric ammonium nitrate have been used.
~ The nitrate salt component o~ the present invention must be present in a form within the imaging 5~g6 layer so ~hat oxidizing quantities of HNO3, NO, NO2, or N204 will be provided within thP layer when it is heated to a temperature no greater than 200C ~or 60 seconds and preferably no greater than 160C for 60 or mo~t pre~erably 30 seconds. this may be accomplished with many dif~erent types of salts, both organic and inorganic, and in variously different types of constructions.
The most convenient way of providing such thermal oxidant providing nitrate salts is to proivde a hydrated nitrate salt such as aluminum nitrate nonahydrate (Al(NO3) 2 9H20) . This salt, when heated in a binder, wlll generate HNO3, ~O~ NO2 and/or N2O4 in various amounts~
The binder should not be at such a high pH that the libera~ed nitric acid would be immediately neutraliz~d as ~his would adversely a~ect the oxidizing capability o~
the system. It is not essential that a completely acidic or neutral pH environment be provided, but p~ levels above 8.5 may in many cases completely prevent oxidation. It is therefore desired that the nitrate salt containing layer have a pH less than 7.5, preferably equal to or les~ than 7.0, and more pre~erably equal to or less than 6.5.
In addition to hydrated nitrate salts, non-hydrated salts in layers having a pH less than 7.5, and preerably in an acidic environment are a}sv capable of providing HNO3, NO, NO2 and/or N2O4 in sufficient quantities to provide the oxidizing capability necessary for practice of the presen invention. Ammonium nitrate, for example, does not enable good oxidation in th~ present invention in a layer having a pH of 8~0 or higher, but 30 when a moderate s rength organic acid such as phthalic acid is added to lower the pH to below 7.0, a ~uite acceptable imaging system is provided.
Beside the inorganic types o~ salts generally desribed above, organic salts in non-alkaline environments 35 are also quite useful in the practice of ~h~ presen~
invention. Xn particular, nitrated quaternary ammonium salts such as guanadinium nitrate work quite well in acid ~L~5~

environments, but will not provide any useful image at alkaline pH levels of 8.0 or higher.
It is believed that the alkaline environme~t causes any oxidizing agent (e.g., HNO3, NO, NO2 and/or N2O4) which is liberated from ~he ni~rate salt to be preferentially reacted with hydroxy ions or other neutralizing moieties so as to prevent oxidation of the dyes. For this reason it is preferred to have ~he environment of the nitrate salt at a pH no greater than 7.0 and more pre~erably less than 6.5.
One other consideration should be given in the selection of the nitrate salt and that is the choice of a salt in which the cation is non-reactive with the dye.
Non-reactive salts are defined in the practice of the present invention as those salts the cations of which do not spontaneously oxidize the dyes that they are asso-ciated with at room temperature. ~his may be readily determined in a number of fashions~ For example, the dye and a non nitrate (preferably halîde) salt of the cation may be codissolved in a solution. I ~he salt oxidizes the dye spontaneously (within two minutes) at room tempera-ture, it is a reactive salt. Such salts as ~ilver nitrate, in which the cation is itself a strong oxldizing agent, is a reactive salt. Ceric nitrate is al50 reactive, while hydrated cerous nitrate is not.
Preferred salts are the hydrated metal salts such as nickel nitrate hexahydrate, magnesium nitrate hexahydrate, aluminum nitrate nonahydrate, ferric nitrate nonahydrate, cupric nitrate trihydrate, zinc nitrate hexahydrate, cadmium nitrate tetrahydrate, bismuth nitrate pentahydrate, thorium nitrate tetrahydrate, cobalt nitrate hexahydrate, gadolinium or lanthanum nitrate nonahydrate, mixtures of these hydrated nitrates and the like.
Non-hydrated or organic nitrates may be admixed therewith.
Organic ni~rates are also quite useful in the practice of ~he present invention. These nitrates are usually in the form of quaternary nitrogen containing compounds such as guanadinium nitrate, pyridinium nitrate, S~9~

and the like. Nitra~ed dy~s will also be useful, but again, they must be used in an environmen~ which will not neutralize any liberated HNO3l NO, NO2, and/or N2O4, It is perferred to have at least 0.10 moles of nitra~e ion per mole of dye~ It is more preferred to have at least 0.30 or 0.50 moles of ion per mol~ of dye. ~ven amounts of form 1.0 to 100 mo:Les of nitrate ion per mole of dye have been found use~ul,, With dyes having relatively higher oxidation potentials, more nitrate i~
10 desirable.
~es The dyes which are u~eful in the d~colorizable systems of the present invention are any bleachable dye.
In some constructions it may be preferable to u~e ~hose 15 which have an oxidation potential of le~ than or equal to ~1Ø These dyes may be selected ~rom any class of dye~.
These classes include but are not limited to methines, indamines, an~hraquinones, triarylemethanes, benzylidenes, monoazos, oxazines, azines, thiazines, xanthenes, indigoids, oxonols, c~aninest merocyanines, phenols, naphthols, pyrazolones, and others, of whioh most are c~assified by the Colour Index System~
The measurement o oxidation potentials is well known to the ordinarily skilled artisan. The measurements in the present invention are taken by measuring th~
voltage and current transferred between a carbon and a platinum electrode through the appropriate solution. 0.1 lithium chloride in anhydrous methanol with 1 to 10 millimoles/liter o~ the appropriate dye was the standard 30 solution used in the measurements given herein with a sa~urated calomel electrode.
It is pr~erred to have suficient decolorizable dye in the binder prior to imaging so ~hat at least 15% of incident radiation (including ultraviolet and i~fra~ed) in 35 a 50 nm range would b~ absorbed ~hrough a 0.5 mm layer of binder and dye. Pre~erably at least 50 or 75~ o~ the incident radiation in a 20 nm range would be absorbedO

1~54g~6 These ranges must of course be chosen within ~he spectral absorption region o~ the particular dye, but such absorption in any portion of the spectra is useful. In terms o~ weight percentages, it would be preferred to have 5 at least 0.30% by weight of either colorizable (i.e., leuco dye) or decolorizable dye as compared to the binder.
Preferably, at least 0.50% by weight of dye to binder is desired and most pre~erably there should be at least 1~ by weight of dye to binder in the layer up to 10% or more.
Leuco dyes are well known in ~he art. These are colorless dyes which when subjected to an oxidation reaction form a colored dye. These leuco dyes are well known in the art ~e.g., The The~r~ the Photogra~hic Process, 3r~ Ed., Mees and James, pp~ 283-4, 390-1, 15 Macmillion Co., N.Y.; and Light-Sensitive Systems, Kosar, pp. 367, 370-380, 406 (1965) Wiley and Sons, Inc., M.Y.).
~nongst the best known leuco dyes are leuco malachite blue, leuco crystal violet, leuco malachite green, and 1(2-(1,3,3-trimethylindolyl~)-2-(p-morpholinylphenyl)-20 ethene. Only those leuco dyes which can be converted tocolored dyes by oxida~ion are use~ul in the practice o~
the present invention. Acid or base sensitive dyes such as phenolphthalein and other indicator dyes are not useful in ~he present invention unless they are also oxidizable 25 to a colored state. ~ndicator dyes would only form transient images or would be too sensitive to changes i~
the environment.
The dyes which have been specifically shown to work in ~he decolorizable systems o~ the present inve~tion 30 include bu~ are not limi~ed to the following:

,, ~5~ 6 Me thine s cl-l COOII

> = CH ~ C ~1 = 1' i N /C --N

3~
~7,1 =CH-C~ ~Rl I:L
wne re in ~C -- N

=S;

~;~ ~ 5031~;

C~i COOH

N ~,S
~1 1: N

:

, :

~5491~G
g l~S ~l~S

C NH

_/s \~ ~s /f O CEI2CH=CH2 S ~S

N-cH2cH2co2 (~) (C2H5) 3 N~;S

C N

=CHNO2; or =C\

2 2 5 7 15 ; (CH2) 5COOH; C8H17 ; CH2CH ¢I; or R3 = H; C2H50; or Cl R4 C2H5 ; or CH2CH2C6H5 CH 3 ~N ) ~ S ) S
CH3 ¦

III

\I=CH-C- ~ S
N ~ NH

:~V

Cll ~ ~CH-CH=~ > ~S ~S

CH3 ¦~ C-- N ~C~ N~

C~H3 ~CH3 :: [~ \
: ~0 ~ ~ ~ -CH-CH- =CH- <

: ~ CH3 : C~13 VI

: .

5~ 6 Cl C--~

3 0 12115 VII

~ N S
> =CH CH= ~ ~ _ Rl 2 5 0 \C2H5 VIII
wherein l ~ ~
: C - --N
O R~

R2 = H ; -CH2COOH ; or -CH2CH=CH2 ~ -CH--CH-CH-, R2 - IX
~herein Rl = C2Hs ; n-C3H7 R2 :

- 12 ~ ~L~LS~6 3 ) 2 Q ~N ( c ~ 2 ( C:H 3 ) 2N ~ C L(~3~ N ( C113 ) 2 tCH3)2N~ H
C=C--C -C
(CH3)2N--<~ R \R

XI
whe re in Rl ~ H; or -CN

R2 = -CN; or -S02CF3 = R3 3~5> l2 S

wherein XII
Rl = =S;

~S ~//s jC N

=(:ll-G~);

C7~15 :

`'` - :

IS~9~

fH2COOH
~N
~ \FS
~C ~ N--R2 = H; CH3 3 R4 = C2H5 ; CH2CH=CH2 7 or CH2CH2C02C2H5 C2H5 ; -CH2CH-CH~ ; or ;C H

R6 = -CH2COOH ; ~CH2CH=CH2 ; or -(CH2)2S03H

7H-Cal~ 2 C - W

XIII

wherein Rl C2d5 ~ -C7Hls ; or -CH2CH=CH2 ~2 =S ; or =C(CN)2 R3 = -Ca~3 ; or C2 5 wh~rein XIV

'lL'~549~96 C2H5 ; (CE12),20H ; -(C~12)2COOH ; -CH2COOH
Or ( CH 2 ) 3S3 25 ( 2~ 20H; - (CH2) 2COOH; -CH COOH
R3 = H;-CH3; -SCH3; OX C2H5 R~ = H ; _CH3 ; -Br ; or -N (('2H5) 2 R5 = H; -CH3; or -E~r ~-- > =CH--I--CH <6 ~ Rl R2 \~

XV
where in Rl = -C~3; -C2H5 R2 3 (C113) 2~ cM=cll-cl~ (S02C~3) 2 XVI

~>-C3-CH=CH-R

XVIl wherein /s~
~J ;
I (~) - 15 - '11~lLS~
r ~N(CH3)2 ~N FH F NX~3 XVIII

~ F ~ ' 2 5 ) 2 CzH5 XIX

1~cc~ 2 F~13 : XX
wherein ~
R 1 = H ; C 1 ~N(CH3)2 R2 = =CH-CH= C

\~N(C,H3)2 ~F~3 =CH{O~--N(CH3)2 :' i ~
' - 16 ~ L5~9~

= N - N - ~ N -(~ ;

=C-CH=~ ,¦ ¦ ;
7 \/

a CH~OH

=CH-CH=~ N(C2 5)2 R3 = H; Br (CH3)2N~CH=CH-C~i=CH-<~

s XXI
(CH3)2N~ ~N(CH3)2 C-CH-CH=CH-C

3 2 ~. . ~N~(CH3)2 ~ ~ .
XXI I
~.

- 17 - ~L~j4~

> = CH - CH ~ \~

C2~i5 // C2H5 XXI I I
where in R -- S -1 ~ ' ._ __ _ , N ~S

C--N~

~=CH-CH=C ~) ., XXI~

Se ~l ~>=CH-CH= ~ ~ ~ S S
C ~N C N
1 C2H5 // R2 CII~CCO:I

: ~ ~ . XXV
whe re in Rl = -CH3, or CH30-- :
~ R2 = -C2H5; or C7H15 , -: ~

-, : , : :

, .

:: :

- 1 8 - ~ 549~16 ~0,~ >= ~ <~

CH30 C2~l5 CH2C001-1 XXVI

CH CH
3~ =CH-CH=CH-CH=CH- 1~ 3 3 H2~:~ o~ N

J

XXVI I

N ~7J =~,H~N~CH:~)2 .
XXVI I I

C~3 ~0 CH3 0= < ~=CH-CH=CH-~ ~ =0 CH3 0C o~3 CH3 XXIX
'X
, .
' ~

- 19 - ~LS~g~6 C~I 3 O o C~l N D ~\ N
0=~ ll ) 2-~11= C ~=u C H 3 o~3 ~ N
~k XXX

'X7V C2H 5~Cl C2H5 ( CH2 ) 2COOH

XXXI
O CH

(CH3)2N <~-CH=CH-CH~ C

XXXI I
n~ le~

il wherein~ XXXIII

! ~ Rl OH; N 2; N 2 5 X

' ~;

s~g~6 R2 = H , -OH ; -OCH 3 R3 = H; -OH; or -NHC2H5 In d:l ~s ,C 7>_~s~S

3 CH 0~ \

XXXIV

CH

>_~N /5 CH
:: 3 O CH 3 ~ ~ XXXV
, ~

~ ~ ' -~ .
~:

~L~549~6 C --N
Rl ~ \

XXXVI
whe re in H; -CH3; or -C2II5 _ _ _ _ ,__ R2 = H; -C2H5; or -CH2COOH

R3 = =S; or =CHN02 ._ R

N

XXXVII
whe re in ~ ~
:~; :

::
- .
. ~.:: .

~L~5~9~6 Rl ~ H; or CH30-R2 = -C2H5 ; -CH2C02 ( C2 5 ) 3 Xant:hene s H ~)C 1(~) CH~C~NC2l~5 ~C02C2H5 XXXVI I I

Azines : ~CH 3 ( CH 3 ) 2N CH 3 C la 3 XXXI X

Oxazines ( CH 3 ) XL_ 23- ~5~ 96 ( C2H5 ) 2N ~ OU

XLI

C l~

XLII

'rhi azlnes ~N~

XLIII

Azos ~N=N-~-NH2 XLIV

- 24 - ~ S4~6 ~N-N

N=N-~

XLV

{}

XLVI

H2N (~N=N~

OC~3 OCH3 XLVII

02N~}N=N~ /C2H5 XLVIII

Diazos C(CH3)z XLIX
'~X ~

- 2 5 ~ S~9~

Triar~Llm.?i;h.~n e ~;
R2 ,~ 3 ) 2 ~- C

~)( CH 3 ) 2 wherein Rl = H; -N(CH3)2 R2 = H; -Cl C l ~ CH 3 ) 2 (~C
Cl~

.
; LI

Inda ines (CH3)2N~} N= ~ =O
.. - ~
, LII
rx ' ~ ~

~S49.96 - 2~ -The Eollowing two dyes cannot be conveniently classed by the Colour Index System:
O~ N(CH3)2 LIII

S ---S

LIV

Tllese examples are not intended to represent the limits of the present invention. ~ny dye having an oxidation potential of +1.0 or less may work in the present invention. The substituent groups and dye structure are unimportant.

~L~;S~.9~
~ 27 _ The decoloriæable dyes of ~he present invention are preferably colored, tha~ is, having absorbance in the visible portion of the electromagnetic spectrum (approxi-mat.ely 400 to 700 nm), but may also be colorless, having absorbance only or predominate:L~ in the infrared ~700 to 1100 nm) or ultraviolet (310 to 400 nm) portions of he electromagnetic spectrumO The images where colorless dyes are used must then be viewed through a filter, ~y an ultraviolet or in~rared sensitive apparatus, or by som~
enhancement technique.
It can also be stated that there should be sufficient decolorizable dye present in the layers o~ this invention so that an optical density o~ at least 4~1 in the visiblP portions o~ the spectrum i~ present or at least 15% o~ incident colorless light (including ultraviolet or in~rared) is absorbed. It is preferred that an optical density of at least 0~5 or 0~8 be obtained and most preferably that there be sufficient dye 60 that an optical density of at least 1.0 be obtained in the layer. With colorless dyes (e.g., ultra~iolet and infrared absorbing dyes), it is preferred that at least 20~ or 40~ o~ incident radiation be absorbed and most preferably that at least 60% or 90% of the i~cident colorless light within a 20 nm range be absorbed. The leuco dye should be present as at leas~ about 0.3% by weight of the total weight o~ the light sen~itive binder layer, pre~erably at l~ast 1% by weight, and most pre~erably at least 2% to 10~ or more (e.g.~ 15%) by weight of the dry weight of the imageable layer. This weight percent is also useful estimating the minimum amount or the decolorizable dyes.
The proportions of nitrate ion and decolorizable dye should be such that on heating the layer at ~60F
~127C~ for 3() seconds there is at least a 20~ reduction 35 in optical density in exposed areas of positive acting systems or unexposed areas in negative acting systems.
With a mechan:ical viewing of the image9 a lower reduction in optical density is useful. Depending upon the relative ease o~ decolorizing the particular dye selected, the relative proportion of nitrate ion to dye may vary. As a general ruler at least 0.1 moles of nitrate ion per mole of dye (whether colorizable ~i.e., leuco dye) or decolorizable) is desirable in the practice o~ the present invention. At least 0.3 or 0~5 moles of nitrate per mole o~ dye is more preferred, and at least 0.7 or 0.9 moles of nitrate per mole o~ dye is most preferred. It is usually desired that the decolorizable layers of the present invention provide more than a 20% reduction in optical density upon exposure and development. At least 50% or 60~ is pre~erred and at least 90% or 95~ reduction in optical density is most pre~erred r~hese reductions can be measured at the development temperatures for the imaging materials, e.g., 130C for 60 seconds or 155C ~or 45 seconds.
The acids optionally useful in the present inven-tion are acids as generally known to the skilled chemist.
Organic acids are preferred, but inorganic acids ~generally in relatively smaller concentrations) are also useful. Organic acids having carboxylic groups are more preferred. The acid may be present in a ratio of from 0 to 10 times the amount of the nitrate ion. More preferably it is present in amounts from 0.2 to 2~0 time~
the amount o~ nitrate ion.
In ~orming or coating imageable layers onto a sub~trate, temperatures should, of course, not be used during manu~acture which would completely colorize or 30 decolorize the layer or decompoæe the diazoniwm salts.
Some colorization or decolorization is tolerable, with the initial dye or leuco dye concentrations chosen so as to allow for anticipated changes. It is pref~rred, however, that little or no leuco dye or dye be oxidized during 35 forming or coating so that more standardized layers can be formed. Depending on ~he anticipa~ed development tempera-ture, the coating or forming temperature can be varied.

,.

~49~
_ 29 -Therefore, if ~he anticipated development temperakure were, for example, 350F (1~7C), the drying temperature could be 280F ~138C). It would therefore not be likely for the layer to gain or lose too much of its optical density at ~he drying temperature in less than 4-5 minutes. Such a change might be tolera~le by correspondingly increasing th~ amount of leuco dye or dye.
A reasonable development temperature range is between 180~F (82C) and 380~F ~193C) and a reasonable dw~ll time is between 5 seconds and 5 minutes, preferably at between 220F (105C) and 350~F (167C) and for 10 to 180 seconds, with the longer times most likely associated with the lower development temperatures. Therefore, the absorbance characteristics should be considered in relationship to the generally use~ul development range of 82C to 193C.
Light sensitive diazonium salts are well known in the art. These ~alts comprise a light sensitive aromatic nucleus with an external diazonium group a~d an anion associated therewith (e.g., Light-Sen itive ~YC~
Kosar, pp. 202-214, John Wiley and Sons, Inc. l9S5, N.Y.;
and Photographic Chemistry, Vol. II, P. Glafkides~ pp.
709-725, Fountain Press, London). They may be generally represented by the formula:
ArN N X
wherein Ar is an aromatic nucleu~, and X is an anion.

Any anion may be used on the diazonium salt. Anions as diverse as zinc chloride, tri-isopropyl naphthalene sulfonate, fluoroborate (i.e., BF4 ), and bis(perfluoro-alkylsulfonyl)methides may be used. The change in anions may aE~ect the speed o~ the imaging layer, but not its function. Any light sensitive aromatic diaæonium nucleus, as known in the art, may also be used in the practice of the present invention. Thes~ nuclei are well known in the 35 art and include, for example P anilinobenzene;
N-(4-diazo-2,~- dimethoxy phenyl)pyrollidine;

9~
- 30 ~
l~diazo-2,4-diethoxy-4- morpholino benxene;
l-diazo-4-bellzoyl amino-2, ~-diethoxy benzene;

4-diazo--2 ,5-dibutoxy phen~1 morpholino; 4-diazo l-dimethyl aniline; l-diazo-N,N-dimethyl aniline;
3-methyl- 4-pyrollidone benzene;
l-dia~o-4-N-me~hyl-N-hydroxyethyl aniline; etc. Light sensitive oligomeric diazonium resins as known in the art (e.gO, U~Sc Patent No. 2,714,066) are U8e~Ul and are specifically included within the definition o~ diazonium salts as they are merely condensation products o~ the salts (with aldehydes such as :eormaldehyde) and re~aln their light sensitive and active proper~ies. ~hese s~lt~
~hould be present as at least about 0.1~ by wei~h~ of the dried imaging layer up to 15% or more. Prefer~bly they are present as ~rom 0.3 ~- 10% by weight of the layer and most preferably as O.S - 5% by weight of the layer and in at least equal molar proportions to the dye or leuco dye.

Additional ingredients such as surfactants, antistatic agents, flow control aids , antioxidants ( eOg ., hindered phenols, phenidone, and ascorbic acid), and other general aids may be present in the imaging layer.
All of this will be more ~horoughly understood by consideration o~ the following examples:

xamples 1-18 A reference coating solution was prepared by mixing 66.67 g o a 15% solution of cellulose acetate butyrate (in a solvent ~olution comprising 10 parts methylisobutylketone, 20 par~s methanol, and 55 parts acetone) with 0~05 9 phenidone A, 0.15 g phthalic acid, 0.49 g benzotriazole, 0.38 g of 1-diazo-2,5-dimethoxy-4-morpholinobenzene zinc chloride, 0.335 g leuco crystal violet, 4.43 9 methanol, 12.50 g acetone, and 5.00 g tetra11ydrofuran. .he indicated weight of each nitrate shown in the table below was dissolved in methanol to a total weight of 1 g, and this was added to 9 g of the ~5~9~6 re~erence coating solution. Each ~inal solution was coated at 4 mils wet thickness onto polyethylene terephthalate ~ilm and dried for ~our minutes at 71C.
Each coated film was imagewise exposed to ultraviolet light until the diazonium salt in the light struck areas was decomposed. One portion of each film was developed at 99C and another sample was developed at 139C for various times, visually determining when optimum development occurred. The optical density in the light struck ~LS) areas and the non-ligh~ struck (NLS) areas was record~d.
The results appear below, with all developing times ~Dev.
Time) reported in seconds.

4~6 ~ - 32 -.:~
E~ u~ o o o o ~n o o o o o ~Y N r l _ ~ 00 1~ r o a~ ~ o ~ _ _ v U~ r1 ~r'~
rl -.~ Or~ O O O O O ~ r~ ~

Et 1~') 10 Q
'J- t~ l ~
8 ~

co o~ u~ o o cr~
o o ~ ~ o a~ ~
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'115~9~6 3~ -In addition to the showing of general utility ~or all the various ~orms of nitrate ion, certain unusual characteristics can be seen. Most examples showed only modest or negligible negative image formation upon heating to 99C. Most examples showed positive image formation upon heating to 139C. Thus either posi~ive and neyative images may be produced ~rom most o the imaging systems of the present inven~ion depending upon development temperatures.

Examples 19-45 Two separate solutions were prepared. One comprised 0.23 g Al(N03)3-9H20 in 19.77 g methanol. The other was identical to the re~erence solution a~ exampl~s 1-18 except that no diazonium salt was present and only 3.81 g of methanol was added (excluding that already with the resin). Various dia~onium salts, in equimolar proportions with the dye, were added to the nitrata solution and dissolved. Two grams ~ this was then combined with 8 grams o~ the dye containing solution and coated and dried as in the previous examples, The ~ame exposure, developments, and recordings were made as in the previous examples, and the results are shown below.

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l~g49~6 Again, the results show general utility for light sensitive diazoniwn salts. Some are clearly more efEective than others, and again both negative and . positive imaging can be produced.

Exam~ s 46-55 A nitrate solution comprising 0.23 g Al(N03)3 9H20 in 19.77 g methanol was prepared. The selected diazonium salts were added to this ~olution to form 2 g portions which were then added to ~ g portion~ of the reference co~ting solution o~ Example~ 19~-45. These were then coated and dried as in the previou~ examples.
Again, the diazonium salts were in approximately equimolar proportions to the dye. The coated film was exposed, developed, and evaluated as in the previous examples.

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o ~5~9~6 ~ ~3 ~ e 55 A light sensitlve system according to the present invention was constructed in the following manner.
A solution was prepared by mixing the folloiwng ingredients:
0.01 g phenidone A (l-phenyl-3-pyrazolidinone~ a reducing agent used as a qtabilizer, 0.10 g benzotriazole (a ~tabilizer), 0~03 g bis~perfluoromethylsul~onyl)methane ( CF3S2 ) 2CH2 0.06 g l diazo-2,5-diethoxyphen~Yl morpholino tetrafluoroborate 1.0 g acetone 0.70 g of a 4.76~ by wei~ht solution of Ni(NO3~2-6H2O in methanol, 3.2 g o~ a 2.15~ by weight solution o~ leuco crystal violet in acetone, and 15.0 g of a 15~ by weight solids solution o~
cellulose acetate butyrate in a 10:20:50 solution of methylisobutylketonet methanol and acetone respectively.

This solution was coated on polyester at 3-1~2 mils wety then dried for four minutes at 71C. The drie~ coated film was ima~ewise exposed to ultraviolet radiation to decompose the diazonium salt in the imaged areas. ~he exposed film was then developed by heating to 139C on a heated roller.
A strong negative image was produced where the color density was yreatest where light struck.

5~9~6 Example 56 Three solutions were prepared. Th~ ~irst was Of 0.10 g Crystal Violet, 5 ml o~ methanol, and 5 ml of N-methyl-pyrrolidone. The second solution waa made from 4 g magnesium nitrate hexahydrate (Mg(NO3)2-~H203 and 75 ml of methanol. The third solution comprised 20 g cellulose acetate, 10 ml methyl isobut~l ketone, and 70 ml acetone.
3 ml o the first solution was mixed with 3 ml of the second solution an 12.5 g of the third solution. To this was added 0.03 g o~ 3-msthyl-4-pyrrolidino-benzene tetrafluoroborate. This solution was coated onto clear polyethylenetereph~hala~e film at 4 mils wet thickness and dried ~or 4 minutes at 70C.
The dried film was imagewise exposed ~o ultraviolet light until the diazonium salt had be2n decomposed in the light struck areas. Upon hea~ing to 130C for 40 seconds, a readable image developed. The dye was bleached far more in the light struck areas than in the non- light struck areas~ providing a positive image.

Example 58 The previous example was duplicat d except that an equal weight o~ Malachite Green was used in place of the Crystal Violet. Substantially similar results were obtained, although a less dense image wa~ produced with the Melachite Green as compared to the Crystal Violet.

Exam~le 59 Example 55 was duplicated except that an equal weight o~ the leuco dye 1(2-(1,3,3-trimethylindolyl)~-2-~p-morpholinylphenyl)ethene was used. A substantially similar result was ob~ained, except that the image was, negative, red and somewhat less dense.

xample 60 Example 55 was duplicated except that an e~ual molar amount of leuco malachite green was used in place of ~s~
- ~5 -the leuco crystal violet. A green positive image was produced after exposure and development as in Exarnple 59.
Example 61 Example 55 was duplicated except an equal molar amount of the leuco dye CH3_ C - ~ -C -CH3 C ~ O
I

(CH3)2N NtCH3)2 was used in place of leuco crystal. A light blue positive image was produced after exposure and development as in Example 55.
It is important to note that the phenomena by which imaging occurs is not understood. Even the positive or negative nature o the imaging system cannot be predicted. For example, the imaging sheet of Example 61, ;~ 20 when left at ambient conditions for three days and then exposed and developed, produced a negative image.
.

Example 6?
Example 55 was repeated except that the cellulose acetate butyrate solution was replaced with 15 g of a 30~ by weight solution of celluIose aceta~e propionate in a 10:20:40 solution of the same solvents respectively. When imaged and then developed at 9~ C, a strong negative image was produced.
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Example 63 Example 55 was repeated except that equimolar proportions Oe the Eollowing dyes were used in place o~
the leuco crystal violet:
63. Dye No. I
64. Dye No. II wherein Rl is N ~ ~S

~ -N~ -and R2 is C2H5 65. Dye No. III
66. Dye No. IV
67. Dye No. VI

6~. Dye No. VII
69. Dye No. IX
70. Dye No. XI
71. Dye No. XIII wherein R1 is C2H5, r2 is S and R3 is CH3 72. Dye No. XVI
73. Dye No. XXI
74. Dye No. XXVII

7 5. Dye No. XXX
76. Dye No. XXXI wherein Rl is NH2, R2 and R3 are H
77. Dye No . XXX IV
78. Dye No. XXXVIII
79. Dye No. XXXIX
80. Dye No. XL
81. Dye No. XLIII
82. Dye No. XLIV
83. Dye No. X~VII
84. Dye No. XLIX
~5. Dye No. L.tI
No other light-sensitive agents are necessary in the constructions o~ the present invention beyond those described in order to provide good q~ality images. Other iL~L54~6 components besides those specifically described may of course be added to the systems when found useful. The sheets were coated and drie!d as in Example 55. Each of the coated polyester sheets were initially colored due to the presence of the dye. E:xposure and development was the same as in that Example, but the images were now generally positive images, with the color density the lowest where light struck.
The imaging layers of the present invention must allow reactive association amongst the active ingredients in order to enable imaging. That is, the individual ingredients may not be separated by impenetrable barriers within the layer, as in dispersed immiscible phases.
Generally, the active ingredients are homogeneously mixed (e.g., a molecular mixture of ingredients) within the layer. They may be individually maintained in heat softenable binders which are dispersed or mixed within the layer and which soften upon heating to allow migration of ingredients, but this would require a longer development time.
The imaging layers of the present invention may contain various materials in combination with the essential ingredients of the present invention. For example, lubricants, coating aids, antioxidants (e.g., ascorbic acid, hindered phenols, phenidone, etc. in amounts that would not prevent oxidation of the dyes when heated), surfactants, antistatic agents, mild oxidizing agents in addition to the nitrate, and brighteners may be used without adversely affecting practice of the invention.
The imaging layers of the present invention must allow reactive association of the active ingredients in order to enable imaging. That is, the individual ingredients may not be separated by impenetrable barriers within the layer, as with dispersed immiscible phases.
Generally, the active ingredients are homogeneously mixed (e.g~, a molecular mixture of ingredients) within the 3~

layer. They may be individually maintained in heat softenable binders which are dispersed or mixed within the layer and which soften upon heating to allow migration of ingredients, but this would require a longer development time.
A reasonable basis for determining the acidity of the coating composition (e.g., whether it is below a pH
of 7.0 as described herein) is to evaluate the stability of a specific diazonium salt in the composition. Using the specific salt of Example 19, if more than 25% by weight of the diazonium salt decomposes, the pH is probably too much above 7Ø
One noteworthy property of this system is amplification of the latent image. By amplification in the leuco dye containing construction is meant that more than one molecule of dye is formed for each absorbed photon of radiation. The degree of amplification, that is the ratio of the number of dye molecules formed to photons absorbed, may be as high as l x 103.

Claims (17)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An imageable composition comprising a) a polymeric binder, b) a bleach-able dye or a leuco dye, c) a non-reactive nitrate salt, d) a photosensitive diazonium salt, and e) an acid, said nitrate salt in said imageable composition being capable of liberating HNO3, NO, NO2 or N2O4 is oxidizing amounts when said composition is heated to no more than 200°C for 60 seconds.

2. The composition of claim 1 wherein a leuco dye is present as at least 0.3% by weight of the composition, the nitrate salt is present in a molar ratio to the leuco dye of at least 0.1 nitrate/1.0 dye, the diazonium salt is present as at least 0.1% by weight of the composition, and the binder comprises at least 25% by weight of the composition.

3. The composition of claim 1 wherein a bleachable dye having an oxidation potential of less than +1.0 is present so that there is an optical density of at least 0.1 in the composition from the dye, and the nitrate ion is present in a molar ratio to the dye of at least 0.1 nitrate/1.0 dye.

4. The composition of claim 1, 2 or 3 wherein an organic carboxylic acid is also present in said composition.

5. The composition of claim 1, 2 or 3 wherein the nitrate ion is present as a metal nitrate salt.

6. The composition of claim 1, 2 or 3 wherein the salt nitrate salt is present as a hydrated metal nitrate salt.

7. The composition of claim 1, 2 or 3 wherein said nitrate salt is a hydrated metal nitrate salt of at least one of the group consisting of zinc, cadmium, nickel, aluminum, iron, tin, copper, magnesium, chromium, cobalt and calcium.

8. The composition of claim 2 wherein said leuco dye comprises at least 1% by weight of said composition and said nitrate salt provides at least 0.5 moles of nitrate ion per mole of leuco dye.

9. The composition of claim 3 wherein said bleachable dye is at least 1%
by weight of said composition and said nitrate salt provides at least 0.5 moles of nitrate ion per mole of dye.

10. The composition of claim 8 wherein said leuco dye is selected from the class consisting of leuco crystal violet, leuco malachite green, leuco malachite blue, and 1(2-(1,3,3-trimethylindolyl))-2-(p-morpholinylphenyl)ethene.

11. The composition of claim 10 wherein the nitrate salt is a metal nitrate salt.

12. The composition of claim 11 wherein the nitrate salt is present as a hydrated metal nitrate salt.

13. The composition of claim 8 or 10 wherein said binder comprises at least 70% by weight of the imageable composition.

14. The composition of claim 1, 2 or 3 wherein said binder comprises at least 70% by weight of the imageable composition.

15. The composition of claim 1, 2 or 3 wherein said nitrate salt is a hydrated metal nitrate salt of at least one of the group consisting of zinc, cadmium, nickel, aluminum, iron, tin, copper, magnesium, chromium, cobalt and calcium and said binder comprises at least 70% by weight of the imageable com-position.

16. The composition of claim 1, 2 or 3 wherein an antioxidant is present.

17. The composition of claim 8 wherein an antioxidant is present.