Stabilization of photosensitive recording material

A recording process including image stabilization comprising the steps of: PA1 1. image-wise exposing to active electromagnetic radiation of a recording material containing in a recording layer a dye precursor compound and at least one photosensitive organic polyhalogen compound capable of producing photoradicals and a dyestuff with said dye precursor compound when exposed with ultraviolet radiation and/or visible light, and PA1 2. heating the photoexposed recording material thereby transforming the non-decomposed polyhalogen compound into a non-photosensitive substance by reaction with at least one stabilizing substance selected from the group consisting of triphenylamine, A soft base containing an element of the group consisting of phosphorus, arsenic, antimony, bismuth, selenium, and tellurium, and an .alpha.,.beta.-ethylenically unsaturated compound in which at least the .alpha.-carbon atom of at least one ethylene group is linked to cyano, a cyanomethyl group, an acyl group, an acyloxy group, an alkoxycarbonyl group, a carbamoyl group or an aryl group, said stabilizing substance(s) being available in a layer adjacent to the recording layer for allowing on heating the reaction with non-photo-decomposed polyhalogen compound.

The present invention is directed to a recording method for forming a 
permanent or stabilized image resulting from the information-wise exposure 
of a free radical photo-sensitive material as hereinafter defined, wherein 
said method includes the inactivation of the photosensitivity of the 
compound producing the free radical. 
By the term "free radical photosensitive material" employed in the present 
description is meant a photosensitive material in which at least one of 
the photosensitive ingredients is an ultraviolet and/or visible light 
sensitive organic polyhalogen compound producing photoradicals on exposure 
with said radiation. 
Photographic dye-forming systems based on the use of said polyhalogen 
compound and a dye precursor compound have been described, e.g., by R. A. 
Fotland in J. Phot. Sci., 18 (1970), 33-37, in the U.S. Pat. Nos. 
3,102,810 and 3,377,167, the United Kingdom Pat. Nos. 1,151,578 and 
1,073,345 and in the Belgian Pat. Nos. 771,848; 786,973; 787,339 and 
790,340 corresponding with the United Kingdom Pat. application Nos. 
41,749/70, 40,349/71, 42,802/71 and 48,804/71 respectively. 
In all these dye-forming systems carbon tetrabromide and/or iodoform are 
the most commonly used photoradical-generating compounds because these 
compounds excel in photosensitivity when compared with other 
representatives of the class of photosensitive organic polyhalogen 
compounds. 
One of the presently known stabilization techniques makes use of the 
volatility of the carbon tetrabromide, which can be removed from the 
non-exposed portions of the recording material relatively easily by 
evaporation. A suitable stabilization temperature is, e.g., in the range 
of 100.degree. to 150.degree. C. 
The evaporation of carbon tetrabromide in the environment of the operating 
personel poses, however, a problem since the compound is physiologically 
not inert and classified as being toxic (see I. Sax, Dangerous Properties 
of Industrial Materials (1968)). 
The toxicity problem still remains when applying another commonly used 
stabilization technique that is based on the extraction of the 
photosensitive polyhalogen compound. 
In the known extraction-stabilization technique a solvent for the 
photosensitive polyhalogen compound is used, which solvent does not affect 
or only weakly affects the binding agent of the recording layer. Some 
solvents such as diethyl ether, although being excellent extraction agents 
cannot be used for the risk of explosion. Other suitable extraction 
solvents belonging to the class of liquid halogenated aliphatic 
hydrocarbons are not miscible with water and must not be drained off in 
the sewer. 
Now a recording process has been found including image stabilization 
comprising the steps of: 
1. image-wise exposing to active electromagnetic radiation a recording 
material containing in a recording layer a dye precursor compound and at 
least one photosensitive organic polyhalogen compound capable of producing 
photoradicals and a dyestuff with said dye precursor compound when exposed 
with ultraviolet radiation and/or visible light, and 
2. by heating transforming the non-decomposed polyhalogen compound into a 
non-photosensitive substance by reaction with at least one stabilising 
substance selected from the group consisting of triphenylamine, 
a "soft-base" containing an element of the group consisting of phosphorus, 
arsenic, antimony, bismuth, selenium and tellurium. 
and an .alpha.,.beta.-ethylenically unsaturated compound in which at least 
the .alpha.-carbon atom of at least one ethylene group is linked to cyano, 
a cyanomethyl group, an acyl group, an acyloxy group, an alkoxycarbonyl 
group, a carbamoyl group or an aryl group, said stabilizing substance(s) 
being available in a layer adjacent to the recording layer for allowing 
the reaction with non-photo-decomposed polyhalogen compound on heating. 
By the wording "soft base" is understood in the present invention a 
substance whose logarithm of the reaction rate constant of the reaction of 
the base with the trans-Pt (C.sub.5 H.sub.5 N).sub.2 Cl.sub.2 complex is 
lager than 3. Soft bases having that property are described in Science 
151, 172-7 (1966) and in J. Chem. Educ. 45, 581-587 (1968) more 
particularly in Table 3 of the article "Acids and Bases, HSAB" by Ralph G. 
Pearson. 
The present invention includes further an integral copy material containing 
the photosensitive polyhalogen compound and stabilizing agent out of 
direct chemical contact from each other at room temperature 
(20.degree.-30.degree. C.) but in such a condition that reactive contact 
is effected through heating of the material at a temperature above 
60.degree. C. 
In the integral copy material system different techniques of keeping the 
polyhalogen compound and the "soft base" and/or sterically hindered 
phenol out of reactive chemical contact below 60.degree. C. may be 
applied. For example, the reactants are kept out of direct chemical 
contact by enveloping at least one of the reactants in a capsule or 
droplet that contains a shell or envelope of a material, normally a 
polymeric material or wax that prevents the direct contact with the other 
reactant. The capsule shell or droplet envelope is ruptured of softened by 
heating, as a result of which the reactants enter into reactive contact. 
Preferred integral copy materials applied in the present invention contain 
the photosensitive organic polyhalogen compound and stabilizing substance 
out of chemical reactive contact at least below 60.degree. C. in apart 
binder layers in which the layer containing the stabilizing substance is a 
layer adjacent to the layer containing the polyhalogen compound and is 
applied from a solution in a volatile liquid, which is a non-solvent for 
the polyhalogen compound and the binder contained in the imaging layer 
comprising the polyhalogen compound and dye precursor compound. Premature 
reaction is avoided effectively when in a first layer on the support, e.g. 
resin support, of the recording material a vinyl carbazole homopolymer or 
copolymer binder containing the dye precursor compound, e.g. a spiropyran 
compound and polyhalogen compound and being insoluble or poorly soluble in 
ethanol or methanol, is coated and the stabilizing substance is applied in 
a polymeric binder that is highly soluble in ethanol. Preferred binders 
for the covering layer are cellulose nitrate, polyvinyl acetate, 
ethylcellulose and polyvinylbutyral. 
If coated on a removable carrier, the very vinylcarbazole polymer or 
copolymer film containing the dye precursor compound and polyhalogen 
compound may serve as the support but preferably it is permanently 
supported on a separate heat-resistant film, e.g. a polyester resin film, 
preferably a polyethylene terephthalate film. The ratio of vinyl 
carbazole, homopolymer or copolymer to dye precursor compound in the 
integral sheet system material may be in the range of about 20 to 2 parts 
by weight of polymer to 1 part by weight of dye precursor compound. 
The triphenylamine and "soft base" stabilizing agent are preferably 
present in the recording material at least in equimolar amount with 
respect to the photosensitive polyhalogen compound. 
The molar amount of .alpha.,.beta.-ethylenically unsaturated compound is 
preferably at least 2 times as large as the molar amount of the 
photosensitive polyhalogen compound in the recording material. 
If plasticizers are used in the layer containing the triphenylamine, "soft 
base" and/or .alpha.,.beta.-ethylenically unsaturated compound preference 
is given to those that do not opacify the recording material, in other 
words those that are compatible with the binder, e.g. cellulose nitrate. 
The plasticizer should therefore be soluble in the same solvent as the 
binder. It should be essentially non-volatile in normale storage 
conditions. Suitable plasticizers for celulose nitrate are polyalkylene 
glycol and camphor. 
Particularly useful stabilizing agents of the "soft base" type of the 
elements phosphorus, arsenic, antimony or bismuth correspond to the 
following structural formula: 
##STR1## 
wherein: X is phosphorus, arsenic, antimony or bismuth, and 
Ar is an aryl group e.g. a phenyl group. 
The use of such triaryl compounds in a photosensitive mixture containing a 
leuco dye compound and a photosensitive organic halogen compound has been 
described already in the United Kingdom patent specification No. 
1,161,058. 
Preferred stabilizing agents of the "soft base" type are given in the 
following Table 1 with their structural formula, melting point and 
reference to their preparation. 
Table 1 
______________________________________ 
Melting 
point 
or 
Boiling 
point Preparation 
No. Structural formula 
(.degree. C.) 
ref. 
______________________________________ 
##STR2## 74-76 P. Pfeiffer, Ber. 37,4620(1904) 
2 
##STR3## 200 O. Neunhoeffer, Ber., 94, 2515 (1961) 
3 (CH.sub.3CH.sub.2CH.sub.2CH.sub.2).sub.3 P 
b.p. W. Davies, J. 
150 Chem. Soc., 1929 
(50 mm 33 
Hg) 
4 
##STR4## 50 G. Hiers, Org. Synt. Coll. Vol. 1 535 
5 
##STR5## 127 T. Talalaevce J.Gen. Chem. U.S.S.R. 16 
777 (1946) 
6 
##STR6## 
##STR7## 
H. Leicester, Org. Synth. Coll. Vol. II, 
238 
______________________________________ 
.alpha.,.beta.-Ethylenically unsatured compounds for use as stabilizing 
agents according to the present invention correspond to the following 
general formula: 
EQU X--(CH=CH--).sub.n Y 
wherein: 
X represents an aryl group e.g. phenyl, CN, --CH.sub.2 CN, an acyl group 
e.g. benzoyl, an acyloxy group, an alkoxycarbonyl group, an 
aryloxycarbonyl group or a carbamoyl group, 
Y represents hydrogen or one of the groups mentioned under X, and 
n is 1 or 2. 
Preferred unsaturated compounds are given in the following Table 2 with 
their structural formula, melting point and reference to their 
preparation. 
Table 2 
__________________________________________________________________________ 
Boiling point 
(bp) or melt- 
ing point (mp) 
No. 
Structural formula (.degree. C.) 
Preparation ref. 
__________________________________________________________________________ 
1 CH.sub.2CHCN (bp) 78 
C. Monreu, Bull.Soc. 
Chim.France (4) 
27, 903 
##STR8## (bp) 72 
A. Sladkov, J.Gen. Chem. U.S.S.R., 24, 
459(1954) 
3 CH.sub.2CHCH.sub.2 CN (bp) 118 
P. Bruylants, Bull. 
Soc.Chim.Belge 31, 
176 
4 
##STR9## (mp) 125 
Beilstein, E II Vol.5 (1943), 537 
5 
##STR10## (mp) 147 
Beilstein, E II Vol.5 (1943), 589 
6 
##STR11## (mp) 59 
Beilstein, E II Vol.7 (1948), 
__________________________________________________________________________ 
423 
The above mentioned stabilizing agents that are particularly advantageously 
used in conjunction with carbon tetrabromide are also effective in the 
stabilization of photosensitive materials containing photosensitive 
organic polyhalogen compounds other than carbon tetrabromide. 
Photosensitive organic polyhalogen compounds that obtain reduced 
photosensitivity by reaction with the mentioned stabilizing agents are 
within the scope of the following general formula that includes carbon 
tetrabromide: 
##STR12## 
wherein: each of A, B, X and Y is a halogen atom of the group of chlorine, 
bromine or iodine, or 
wherein one of said radicals A, B, X or Y represents an alkyl group, 
including a substituted alkyl group, e.g. a halogen-substituted alkyl 
radical, a hydroxy-alkyl radical or an aralkyl, e.g. benzyl, a quinoxaline 
group, an aryl group, a substituted aryl group, an aroyl group or an aryl 
sulphonyl group and the other radicals chlorine, bromine or iodine, or 
wherein two of said radicals A, B, X or Y represent an aromatic acyl 
group, e.g. benzoyl, and the other radicals chlorine, bromine or iodine. 
Particularly suitable representatives falling within the scope of that 
general formula are organic halides such as carbon tetrabromide, 
bromoform, iodoform, hexachloroethane, hexabromoethane, pentabromoethane, 
1,1,2,2-tetrabromoethane, .alpha.,.alpha.,.alpha.-tribromoacetophenone, 
.alpha.,.alpha.,.alpha.-tribromomethylsulphonylbenzene, and its chlorine- 
or nitro-substituted derivatives, tribromoethanol and the 
2-tribromomethylquinoxaline compounds described in Belgian Pat. No. 
757,145.

The following examples illustrate the present invention without, however, 
limiting it thereto. The parts, percentages and ratios are by weight, 
unless otherwise indicated. 
EXAMPLE 1 
24 Parts of carbon tetrabromide, 24 parts of iodoform, 24 parts of 
3-methyl-di-.beta.-naphthospiropyran, 100 parts of poly-N-vinylcarbazole, 
2 parts of silicone oil dissolved in 1446 parts of trichloroethylene and 
1336 parts of methylene chloride were used for the coating of the imaging 
layer A on a polyethylene terephthalate support of a coverage of 95 ml per 
sq.m. 
The stabilizing layer B was coated on top of layer A in a ratio of 38 ml 
per sq.m with the following composition: 50 ml of a 5% solution of 
cellulose nitrate in ethanol and 50 ml of a 10% solution of 
triphenylstibine in ethylene glycol monomethyl ether. 
After drying, this material was exposed for 20 s to ultraviolet radiation 
in an Actina SH (trade name) diazo copier containing an U.V. lamp of 1000 
W and heated for 8 s at 130.degree. C. A light-stable image was obtained. 
EXAMPLE 2 
On the same imaging layer as described in Example 1 a stabilizing layer was 
coated in a ratio of 76 ml per sq.m with the following composition: 50 ml 
of a 10% ethylcellulose solution in dioxan and 50 ml of a 10% 
triphenylstibine solution in ethylene glycol monomethyl ether. 
After drying, this material was exposed to U.V. radiation, as described in 
Example 1, heated for 30 s at 130.degree. C. (or for 90 s at 120.degree. 
C.). A light-stable image was obtained. 
EXAMPLE 3 
On the same imaging layer as described in Example 1 a stabilizing layer was 
coated in a ratio of 76 ml per sq.m with the following composition: 50 ml 
of a 10% polyvinyl butyral solution in ethanol and 50 ml of a 7% 
triphenylstibine solution in ethylene glycol monomethyl ether. 
After drying, this material was image-wise exposed as described in Example 
1, and heated for 6 s at 130.degree. C. A light-stable image was obtained. 
EXAMPLE 4 
On the same imaging layer as described in Example 1 a stabilizing layer was 
coated in a ratio of 152 ml per sq.m with the following composition: 50 ml 
of a 20% polyvinyl acetate solution in methanol and 50 ml of a 12% 
tritolylstibine solution in benzene. 
After drying, this material was image-wise exposed as described in Example 
1 and heated for 40 s at 130.degree. C. A stable image was obtained. 
EXAMPLE 5 
On the same imaging layer as described in Example 1 a stabilizing layer was 
coated in a ratio of 152 ml per sq.m with the following composition: 50 ml 
of a 20% cellulose nitrate solution in methanol and 50 ml of a 10% 
diphenylselenide solution in methanol. 
After drying, this material was image-wise exposed as described in Example 
1 and heated for 40 s at 130.degree. C. A light-stable image was obtained. 
EXAMPLE 6 
On the same imaging layer as described in Example 1 a stabilizing layer was 
coated in a ratio of 152 ml per sq.m with the following composition: 50 ml 
of a 30% ethylcellulose solution in ethanol and 50 ml of a 12% 
propene-3-nitrile solution in ethanol. 
After drying, this material was image-wise exposed as described in Example 
1 and heated for 40 s at 130.degree. C. A light-stable image was obtained. 
EXAMPLE 7 
On the same imaging layer as described in Example 1 a stabilizing layer was 
coated in a ratio of 152 ml per sq.m with the following composition: 50 ml 
of a 20% polyvinyl acetate solution in ethanol and 50 ml of a 10% 
triphenylphosphine solution in methanol. 
After drying, this material was image-wise exposed to U.V. radiation and 
heated for 40 s at 130.degree. C. A stable image was obtained. 
EXAMPLE 8 
A polyethylene terephthalate support of a thickness of 0.10 mm was coated 
in a ratio of 76 ml per sq.m with the following composition: 50 ml of a 
10% phenolic resin solution in methanol and 50 ml of a 8% triphenylstibine 
solution in ethylene glycol monomethyl ether. On this stabilizing layer a 
light-sensitive layer of the composition of layer A of Example 1 was 
coated but in a ratio of 152 ml per sq.m. 
After drying, this material was exposed to U.V. radiation and heated at 
130.degree. C. for 2 min. A stable image was obtained. 
EXAMPLE 9 
A polyethylene terephthalate support of a thickness of 0.10 mm was coated 
in a ratio of 152 ml per sq.m with the following composition: 12 parts of 
.alpha.,.alpha.,.alpha.-tribromoquinoxaline-2, 12 parts of 
3-methyl-di-.beta.-naphthospiropyran, 50 parts of poly-N-vinylcarbazole, 1 
part of silicone oil, dissolved in 1446 parts of trichloroethylene and 
1336 parts of methylene chloride. 
On top of this imaging layer a stabilizing layer was coated in a ratio of 
76 ml per sq.m. with the following composition: 50 ml of a 10% 
triphenylstibine solution in ethylene glycol monomethyl ether and 50 ml of 
a 10% ethylcellulose solution in methanol. 
After drying, this material was exposed to U.V. radiation and heated for 4 
s at 140.degree. C. A light-stable image was obtained. 
EXAMPLE 10 
A polyethylene terephthalate support of a thickness of 0.10 mm was coated 
in a ratio of 152 ml per sq.m with the following composition: 15 parts of 
carbon tetrabromide, 15 parts of iodoform, 15 parts of 
3-methyl-di-.beta.-naphthospiropyran as dye precursor, 1.5 part of 
Michler's ketone, 50 parts of polystyrene, dissolved in 1446 parts of 
trichloroethylene and 1336 parts of methylene chloride. 
On top of this imaging layer a stabilizing layer was coated in a ratio of 
76 ml per sq.m with the following composition: 50 ml of a 10% 
triphenylstibine solution in ethylene glycol monomethyl ether and 50 ml of 
a 10% ethylcellulose solution in methanol. 
After drying, this material was exposed to U.V. radiation and heated for 30 
s at 130.degree. C. A light-stable image was obtained. 
EXAMPLE 11 
A polyethylene terephthalate support of a thickness of 0.10 mm was coated 
in a ratio of 152 ml per sq.m. with the following composition: 20 parts of 
carbon tetrabromide, 25 parts of 4-p-dimethylaminostyrylquinoline as dye 
precursor, 50 parts of polystyrene dissolved in 1446 parts of 
trichloroethylene and 1336 parts of methylene chloride. 
On top of this imaging layer a stabilizing layer was coated in a ratio of 
76 ml per sq.m with the following composition: 50 ml of a 10% 
triphenylstibine solution in ethylene glycol monomethyl ether and 50 ml of 
a 10% ethylcellulose solution in methanol. 
After drying, this material was exposed to U.V. radiation and heated for 1 
min at 130.degree. C. A light-stable image was obtained. 
EXAMPLE 12 
On the same imaging layer as described in Example 1 a stabilizing layer was 
coated in a ratio of 50 ml per sq.m with the following composition: 35 ml 
of a 10% polyvinylbutyral solution in methanol, 10 ml of ethylene glycol 
monomethylether and 35 ml of a 5% by weight solution in toluol of compound 
4 of Table 2. 
After drying, this material was exposed to U.V. radiation, as described in 
Example 1, and heated for 60 s at 130.degree. C. A light-stable image was 
obtained. 
EXAMPLE 13 
On the same imaging layer as described in Example 1 a stabilizing layer was 
coated in a ratio of 76 ml per sq.m with the following composition: 40 ml 
of a 10% polyvinylbutyral solution in methanol, and 40 ml of a 5% by 
weight solution in toluol of triphenylamine. 
After drying, this material was exposed to U.V. radiation, as described in 
Example 1, and heated for 60 s at 130.degree. C. A light-stable image was 
obtained. 
EXAMPLE 14 
On the same imaging layer as described in Example 1 a stabilizing layer was 
coated in a ratio of 50 ml per sq.m with the following composition: 40 ml 
of a 10% polyvinylbutyral solution in methanol, and 40 ml of a 5% by 
weight solution in ethylene glycol monomethyl ether of compound 6 of Table 
2. 
After drying, this material was exposed to U.V. radiation, as described in 
Example 1, heated for 45 s at 130.degree. C. A light-stable image was 
obtained.