Photographic developing solution containing an ascorbic acid derivative

A photographic developing solution for immersion development is disclosed showing a pH of at least 12.0 and containing more than 0.4 moles/liter of a sugar derivative, or an alkali metal salt thereof, corresponding to general formula (I): ##STR1## wherein X represents an oxygen atom or an imino group, and n represents a positive integer from 1 to 4, and R represents a hydroxy group when n is 1, and R represents a hydroxy group or a hydrogen atom when n is 2 to 4. Preferred sugar derivatives according to the present invention are l-ascorbic acid and iso-ascorbic acid. In a most preferred embodiment there are substantially no other developing agents and no sulphite ions present. When developing a graphic arts photographic material lith quality is obtained. The disposal of depleted solutions can be performed in an ecologically safe way.

FIELD OF THE INVENTION 
The present invention relates to photographic developers and more 
particularly to photographic developers for immersion processing 
containing an ascorbic acid derivative at a high concentration and a high 
pH. 
BACKGROUND OF THE INVENTION 
The developing activity of 1-ascorbic acid (vitamine C) and some chemical 
analogues is known since many years in the photographic art. In their 
report on the synthesis of iso-ascorbic acid (iso-vitamine C or 
d-arabo-ascorbic acid) in Berichte, Vol.67, p. 1239 (1934) Maurer at al. 
for the first time report tests on ascorbic acid and its optical isomer as 
developers for a photographic plate and describe them as active developers 
superior to conventional aromatic developers. However in most later 
studies ascorbic acid and derivatives are regarded as rather weak 
developers by themselves. So there are several publications on developers 
containing a superadditive combination of a conventional developing agent 
and an ascorbic acid derivative used as auxiliary developer or as an 
antioxidant. U.S. Pat. No. 2,688,549 discloses the combination of a 
3-pyrazolidone developing agent and of an ascorbic acid derivative. GB 1 
266 533 describes the combination of a p-hydroxybenzene developing agent, 
an ascorbic acid and sulphite ions. An equally good developing activity 
for both surface and internal latent images is claimed in U.S. Pat. No. 
3,826,654 which discloses a combination of a 3 -pyrazolidone an ascorbic 
acid, a heterocyclic thione or thiol and an alkali iodide at a pH of at 
least 12. The concentration of the ascorbic acid ranged from 0.05 moles to 
0.4 moles per liter. The most preferred pH range was 13 to 14. 
Several compositions specifically for high contrast development are 
published. So U.S. Pat. No. 3,942,985 discloses the combination of an iron 
chelate developer and an ascorbic acid. U.S. Pat. No. 4,756,997 claims a 
combination of a p-hydroxybenzene, an auxiliary developer an antifoggant, 
an antioxidant and an -ketocarboxylic acid wherein the antioxidant can be 
ascorbic acid. 
An application wherein ascorbic acid is the principal developing agent is 
disclosed in the Japanese Unexamined Patent Publication (Kokai) 59-191035 
the reduction or omission of the washing step in the processing cycle is 
claimed as unexpected advantage. The concentration of ascorbic acid ranges 
from 0.2 to 20 g/l in case of immersion processing and from 0.5 to 1OO g/l 
in case of coating development. A pH of 10 to 12 is preferred for 
immersion processing and of 11 to 14 for coating types of development. 
Chemical analogues of ascorbic acid that show developing activity too 
include (iso)ascorbic acid ketals or acetals as disclosed in GB 1 142 135, 
dihydroxyfuran derivatives as described in J. Phot. Sci., Vol. 19 (1971), 
p. 211, and imino-ascorbic acid derivatives as claimed in U.S. Pat. No. 
2,688,548. 
A first study on the kinetics of development by ascorbic acid by T. H. 
James was published in J. Am. Chem. Soc. Vol. 66 (1), p. 91 (1944). The 
results of a more extensive study by Willis and Pontius appeared in Phot. 
Sci. Eng. Vol. 14 (6), p. 384 (1970). The autors concluded to a two step 
mechanism including an induction period and a continuation step with 
different activation energies. 
In graphic and reprographic arts the accurate sharp reproduction of line 
edge and screen dot originals is of uttermost importance. This goal is 
reached by the combination of specially designed graphic arts materials 
and appropriate processing systems producing so-called "lith quality". A 
first group of such processing systems consists of the traditional "lith 
developers" characterized by the presence of hydroquinone as the sole 
developing agent and a low sulphite ions content giving rise to an 
infectious development mechanism. However these conventional developers 
are rather instable in time and require complicated regeneration systems 
for both oxidation and exhaustion. In more recent times so-called "hard 
dot Rapid Access" developers were introduced on the market which combine a 
good stability with a "lith quality" in the reproduction of edges and 
screen dots. Examples of such developers and corresponding appropriate 
photographic materials include the GRANDEX system, marketed by FUJI PHOTO 
Ltd. AGFASTAR, marketed by AGFA-GEVAERT N.V. and the ULTRATEC system, 
marketed by EASTMAN KODAK Co. However all these developer systems show 
some disadvantages from an ecological or toxicological point of view. E.g. 
hydroquinone is a rather unwanted ingredient because of its allergenic 
effects. The biodegradation of disposed Phenidone is too slow. Sulphite 
ions show a high COD (Chemical Oxygen Demand) and the resulting sulphate 
ions are harmful for e.g. concrete. As a consequence it is undesirable 
that depleted solutions of this kind would be discharged into the public 
sewerage; they have to be collected and destroyed by combustion, a 
cumbersome and expensive process. As a consequence residual solutions 
containing sulphite produce emissions containing sulphurdioxide and/or 
sulphurtrioxide on combustion. On the other hand, some "hard dot Rapid 
Access" systems are ecologically suspect due to the presence of hydrazine 
or hydrazide derivatives and/or the presence of amino compounds which can 
be toxic or too volatile as stated in U.S. Pat. No. 4,975,354. It is 
possible that unwanted organic solvents are used in order to introduce 
some water insoluble compounds into the photographic material. Some of 
these suspect compounds can be washed out partially on development. So 
there is a permanent need for developing solutions which can be disposed 
of in a safer way for the environment and which are more 
consumer-friendly. 
In a few cases ascorbic acid is described as showing some activity as a 
"lith developer". In his study on the mechanism of lith development, 
published in J. Phot. Sci. Vol. 27 (1979), p. 185, Zwicky shows that a 
lith effect can occur with ascorbic acid as the sole developing agent and 
he illustrates the effect with photographs showing reproduced line edges 
and contact screen dots. The developing solution employed contained 112 g 
of ascorbic acid per liter, potassium bromide, formaldehyde bisulphite and 
sodium hydroxide to establish a pH of 10.5. However even with this high 
concentration of ascorbic acid the rate of formation of developed silver 
was considerably slower compared to a conventional hydroquinone lith 
developer. As a result the slope of the characteristic or sensitometric 
curve was appreciably lower than with hydroquinone. Eventually no 
commercially usable developer resulted from Zwicky's formula. 
In Miller U.S. Pat. No. 3,386,824 a processing solution of high pH 
containing a high concentration of iso-ascorbic acid is disclosed. However 
this solution is embedded in plastic micro-capsules and not intended for 
conventional immersion processing. 
It is an object of the present invention to provide a processing solution 
which can be treated after use in a safe way for the environment and which 
use is more consumer-friendly. 
It is a further object of the present invention to provide a processing 
solution of a simple composition for immersion processing and easy to 
replenish that produces hard dot quality as an alternative to existing 
lith developers and hard dot Rapid Access developers. 
Further objects will become apparent from the description hereafter. 
SUMMARY OF THE INVENTION 
The objects of the present invention are realized by a developing solution 
for immersion development showing a pH of at least 12.0 and containing 
more than 0.4 moles/liter of a sugar derivative, or an alkali metal salt 
thereof, corresponding to general formula (I): 
##STR2## 
wherein X represents an oxygen atom or an imino group, and n represents a 
positive integer from 1 to 4, and R represents a hydroxy group when n is 
1, and R represents a hydroxy group or a hydrogen atom when n is 2 to 4 
Preferred sugar derivatives according to the present invention are 
l-ascorbic acid and iso-ascorbic acid. In a most preferred embodiment 
there are substantially no other developing agents and no sulphite ions 
present. 
It was shown experimentally that a developing solution of this simple 
composition surprisingly produces a far better lith quality on development 
of graphic arts photographic materials than the composition described by 
Zwicky, cited above. 
It is possible to dispose of used up developing solutions according to the 
invention in a safe way for the environment as will be explained in the 
detailed description following hereafter. 
DETAILLED DESCRIPTION OF THE INVENTION 
Sugar derivatives corresponding to general formula (I) and usable in the 
developing solutions according to the present invention include following 
compounds: 
##STR3## 
The sugar derivatives of this invention are preferaby present in a 
concentration ranging from 0.45 to 0.90 moles per liter. Preferred 
compounds for application in the present invention are l-ascorbic acid and 
iso-ascorbic acid. These compound can be dissolved into the developing 
solution in their free acid form alternatively they can be incorporated as 
an alkali salt, preferably the sodium or potassium salt or a mixture of 
both. In case of the latter method a lower amount of alkali hydroxide is 
needed to establish a pH of at least 12.0. 
In a preferred embodiment of the present invention an alkali bromide salt, 
e.g. potassium bromide is present in the developing solution preferably in 
a concentration ranging from 0.05 moles to 0.8 moles per liter and most 
preferably in a range from 0.1 to 0.4 moles per liter. 
In an other preferred embodiment of the present invention at least one 
so-called antifogging agent or stabilizer is present in the developing 
solution. Numerous chemical classes of stabilizers are known in the 
photographic art. Suitable examples are e.g. the heterocyclic 
nitrogen-containing compounds such as benzothiazolium salts. 
nitroimidazoles, nitrobenzimidazoles, nitroindazoles, 
chlorobenzimidazoles, bromobenzimidazoles, mercaptothiazoles, 
mercaptobenzothiazoles, mercaptobenzimidazoles, mercaptothiadiazoles, 
aminotriazoles, benzotriazoles, nitrobenzotriazoles, mercaptotetrazoles, 
mercaptopyrimidines mercaptotriazines, benzothiazoline-2-thiones and 
oxazoline-thiones. In a preferred embodiment of the present invention the 
antifogging agent is a mercapto-group containing heterocyclic substance 
and most preferably it is 1-phenyl-5-mercapto-tetrazole preferably in a 
concentration range from 10 mg/l to 1 g/l and most preferably in a range 
from 20 to 250 mg/l. 
The rather high pH values in connection with the present invention can be 
established by means of conventional buffering agents but preferably for 
ecological reasons the pH is simply established by the presence of an 
alkali hydroxide, e.g. sodium or potassium hydroxide. The full benefits of 
this invention are obtained in a pH range from 12.3 to 13.5. 
Other adjuvants well known to those skilled in the art may be added to the 
developer liquid of the present invention. A survey of conventional 
developer addenda is given by Grant Haist in "Modern Photographic 
Processing"--John Wiley ans Sons--New York (1979) p. 220-224. Examples of 
such addenda include complexing agents for calcium and magnesium ions, 
present in hard water, e.g. ethylene diamine tetraacetic acid and 
analogues compounds. Further can be present anti-foaming agents, 
surface-active agents, biocides, thickening agent$ like polystyrene 
sulphonate and antioxidants like benzoate and cyclodextrine. The 
developing liquid can contain so-called anti-sludge agents in order to 
reduce dirt streaks on developed photographic material. Finally the 
solution can contain development accelerating agents like 
polyalkyleneoxides and alkonolamines and hardening agents including latent 
hardeners. 
To achieve the optimal sensitometric and dot quality results of the present 
invention there is no need for a second auxiliary developing agent. 
Sulphite ions too can be omitted without detrimental effect on stability. 
So in a most preferred embodiment of the invention there are substantially 
no second developing agent and no sulphite ions present in the developer 
liquid, if needed that second developing agent can be present in the 
photographic material. Thanks to this feature a particular important 
object of the present invention is realized, namely providing an 
ecologically safe solution which can be easily disposed of after use. As 
stated above depleted conventional developers containing 
p-hydroxybenzenes, Phenidones and sulphite ions have to be recollected and 
destroyed by combustion. On the contrary the ascorbic acid derivative 
present in developers of the invention could be recycled for a great part. 
The remainder in the residual solution can be oxidized e.g. by air 
bubbling; in this way the pH can be decreased below 9.0 and the residual 
solution can be discharged into the public sewerage. 
The developing solutions of the present invention can be employed to 
develop various types of photographic black-and-white materials, e.g. 
amateur and professional materials for still photography, radiographic 
recording and duplicating materials, cinematographic recording and 
duplicating materials, and microfilm. However the merits of the present 
invention become most obvious in developing camera or duplicating 
materials for graphic arts in view of the importance of exact reproduction 
of line edge and screen dot originals. 
The emulsions present in these photographic materials can be of any halide 
composition, e.g. bromide, chloride, chlorobromide, iodobromide and 
chloroiodobromide emulsions. The emulsions can belong to the negative 
working type or to the direct positive type, e.g. the externally fogged 
type or the unfogged type requiring a fogging agent in the material or in 
the developing solution. The best results are obtained however when 
applicating the developing solutions of the invention on materials 
containing negative chlorobromide emulsions as is commonly the case in 
various types of graphic arts materials. 
The photographic elements which can be developed by the liquids of the 
present invention can be composed of one single emulsion layer, as it is 
the case for many applications, or they can be built up by two or even 
more emulsion layers. Beside the light sensitive emulsion layer(s) the 
photographic material can contain several non-light sensitive layers, e.g. 
a protective layer, one or more backing layers, one or more subbing 
layers, and one or more intermediate layers, e.g. filter layers. 
The emulsions present in the photographic materials which can be developed 
by the solutions of the present invention can be chemically sensitized as 
described e.g. in "Chimie et Physique Photographique" by P. Glafkides, in 
"Photographic Emulsion Chemistry" by G. F. Duffin, in "Making and Coating 
Photographic Emulsion" by V. L. Zelikman et al, and in "Die Grundlagen der 
Photographischen Prozesse mit Silberhalogeniden" edited by H. Frieser and 
published by Akademische Verlagsgesellschaft (1968). As described in said 
literature chemical sensitization can be carried out by effecting the 
ripening in the presence of small amounts of compounds containing sulphur 
e.g. thiosulphate, thiocyanate, thioureas, sulphites, mercapto compounds, 
and rhodamines. The emulsions can be sensitized also by means of 
gold-sulphur ripeners or by means of reductors e.g. tin compounds as 
described in GB 789,823, amines, hydrazine derivatives, 
formamidine-sulphinic acids, and silane compounds. 
The silver halide emulsions under consideration can be spectrally 
sensitized with methine dyes such as those described by F. M. Hamer in 
"The Cyanine Dyes and Related Compounds", 1964, John Wiley & Sons. Dyes 
that can be used for the purpose of spectral sensitization include cyanine 
dyes, merocyanine dyes, complex cyanine dyes, complex merocyanine dyes, 
hemicyanine dyes, styryl dyes and hemioxonol dyes. Particularly valuable 
dyes are those belonging to the cyanine dyes, merocyanine dyes and complex 
merocyanine dyes. Infra-red sensitizing dyes and combinations with 
supersensitizing compounds can be present. 
The silver halide emulsions under consideration can be stabilized by 
representatives of the same chemical classes which can be present in the 
developing solutions as enumerated above. Other preferred compounds 
include triazaindenes, tetrazaindenes and pentazaindenes, especially those 
described by Birr in Z. Wiss. Phot. 47 (1952), pages 2-58. 
The gelatin binder of these photographic elements can be hardened with 
appropriate hardening agents such as those of the epoxide type, those of 
the ethylenimine type, those of the vinylsulfone type e.g. 
1,3-vinylsulphonyl-2-propanol, chromium salts e.g. chromium acetate and 
chromium alum. aldehydes e.g. formaldehyde, glyoxal, and glutaraldehyde, 
N-methylol compounds e.g. dimethylolurea and methyloldimethylhydantoin, 
dioxan derivatives e.g. 2,3-dihydroxy-dioxan, active vinyl compounds e.g. 
1,3,5-triacryloyl-hexahydro-s-triazine, active halogen compounds e.g. 
2,4-dichloro-6-hydroxy-s-triazine, and mucohalogenic acids e.g. 
mucochloric acid and mucophenoxychloric acid. These hardeners can be used 
alone or in combination. The binder can also be hardened with 
fast-reacting hardeners such as carbamoylpyridinium salts as disclosed in 
U.S. Pat. No. 4,063,952 and with the onium compounds as disclosed in 
European Patent Application No 90.201850.6 
The photographic elements under consideration may further comprise various 
kinds of surface-active agents in the photographic emulsion layer or in at 
least one other hydrophilic colloid layer. Preferred surface-active 
coating agents are compounds containing perfluorinated alkyl groups. 
The photographic elements may further comprise various other additives such 
as e.g. compounds improving the dimensional stability of the photographic 
element. UV-absorbers, spacing agents and plasticizers. 
As stated above the photographic material can contain several non light 
sensitive layers. e.g. an anti-stress top layer, one or more backing 
layers, and one or more intermediate layers eventually containing 
filter-or antihalation dyes that absorb scattering light and thus promote 
the image sharpness. Suitable light-absorbing dyes are described in e.g. 
U.S. Pat. No. 4,092,168. U.S. Pat. No. 4,311,787. U.S. Pat. No. DE 
2,453,217. and GB 7 907 440. One or more backing layers can be provided at 
the non-light sensitive side of the support. These layers which can serve 
as anti-curl layer can contain e.g. matting agents like silica particles, 
lubricants, antistatic agents light absorbing dyes, opacifying agents, 
e.g. titanium oxide and the usual ingredients like hardeners and wetting 
agents. 
The support of the photographic material may be opaque or transparent, e.g. 
a paper support or resin support. When a paper support is used preference 
is given to one coated at one or both sides with an Alpha-olefin polymer, 
e.g. a polyethylene layer which optionally contains an anti-halation dye 
or pigment. It is also possible to use an organic resin support e.g. 
cellulose nitrate film, cellulose acetate film, polyvinylacetal film, 
polystyrene film, polyethylene terephthalate film, polycarbonate film, 
polyvinylchloride film or poly-Alpha-olefin films such as polyethylene or 
polypropylene film. The thickness of such organic resin film is preferably 
comprised between 0.07 and 0.35 mm. These organic resin supports are 
preferably coated with a subbing layer which can contain water insoluble 
particles such as silica or titanium dioxide. 
The photographic material to be developed by the solutions of the present 
invention can be image-wise exposed by any convenient radiation source in 
accordance with its specific application. 
For processing preferably an automatically operating apparatus is used 
provided with a system for automatic replenishment of the processing 
solutions. The developing solution according to the invention has to be 
replenished not only for decrease of the liquid volume due to cross-over 
into the next processing solution but also for pH decrease due to 
oxidation of the ascorbic acid derivative molecules. This can be done on a 
regular time interval basis. e.g. on a daily basis or can be monitored 
automatically by a permanent pH measuring system. 
The development step can be followed by a washing step, a fixing solution 
and another washing or stabilization step. Finally the photographic 
material is dried. The first washing step can be omitted if wanted. 
The following examples illustrate the invention without however limiting it 
thereto.

EXAMPLE 1 
A typical graphic arts chlorobromide emulsion was prepared by a double jet 
technique. The silver halide composition was 83.6 mole % of chloride, 16 
mole % of bromide and 0.4 mole % of iodide, and the average grain size was 
0.27 micron. After addition of inert gelatin the emulsion was chemically 
ripened to an optimal fog-sensitivity relationship and then spectrally 
sensitized to the blue and the green spectral region. 
Finally the emulsion was stabilized by means of 
4-hydroxy-6-methyl-1,3,3a,7-tetraazaindene. After addition of a 
conventional coating aid and a conventional hardener the emulsion was 
coated on one side of a tranparent polyethylene terephtalate support at a 
silver coverage of 6.25 g/m.sup.2, expressed as AgNO.sub.3 /m.sup.2. 
Dried coated samples of the prepared photographic material were exposed by 
a conventional white light source, on the one hand through a continuous 
tone wedge, on the other hand through a contact screen with a ruling of 54 
lines/cm combined with a continuous tone wedge. 
Then these samples were developed on the one hand by means of a solution 
according to the invention (A) and on the other hand by means of a 
conventional hydroquinone-Phenidone control solution (B). The composition 
of the two developers is given in table 1: 
TABLE 1 
______________________________________ 
ingredient Solution A solution B 
______________________________________ 
ascorbic acid 150 g -- 
potassium bromide 25 g 10 g 
1-phenyl-5-mercaptotetrazole 
0.08 g 0.03 g 
hydroquinone -- 20 g 
Phenidone -- 0.5 g 
potassium carbonate 
-- 24 g 
potassium sulphite 
-- 65 g 
potassium hydroxide to 
12.35 10.5 
establish a pH of 
water to make 1 l 1 l 
______________________________________ 
The sensitometric values and screen dot quality ratings after development 
in solutions A and B at 32.degree. C. are represented in table 2. 
TABLE 2 
______________________________________ 
Sol. dev. time fog S.sup.1 
grad(t).sup.2 
grad.sup.3 
dot rating.sup.4 
______________________________________ 
A 20 s 0.04 105 5.3 10 2 
A 30 s 0.05 123 7.0 22 1.5-2 
A 40 s 0.05 132 8.9 29 1.5 
A 50 s 0.06 138 7.2 30 1.5 
B 20 s 0.03 95 3.3 10 &gt;4 
B 30 s 0.03 100 3.3 11 3.5 
B 40 s 0.03 100 3.3 11 3 
B 50 s 0.03 102 3.3 11 3 
______________________________________ 
Notes: 
.sup.1 S: sensitivity measured at density 2.00 + fog and expressed as 
relative arithmetic value whereby the sensitivity for 30 seconds 
development in developer B is arbitrary set to 100; higher value means 
higher sensitivity; 
.sup.2 grad(t).: gradation in the toe of the sensitometric curve measured 
between densities 0.1 and 0.5; 
.sup.3 grad.: gradation measured between densities 1.0 and 3.0; 
.sup.4 dot quality rating expressed in arbitrary units ranging from 0 
(best) to 5 (worst); the values are averages of the ratings for a 10%, a 
50% and a 90% dot. 
The results of table 2 clearly demonstrate the steeper gradation and the 
better dot quality ratings obtained with the developing solution (A) 
according to the invention. 
EXAMPLE 2 
A developing solution according to the invention (C) and control prior art 
solution (D) according to Zwicky's formula were prepared showing following 
compositions (table 3): 
TABLE 3 
______________________________________ 
ingredient solution C solution D 
______________________________________ 
potassium bromide 25 g 18.8 g 
ascorbic acid 150 g 112.5 g 
1-phenyl-5-mercaptotetrazole 
0.1 g -- 
formaldehyde sodiumbisulphite 
-- 37.5 g 
potassium hydroxide to 
12.35 10.5 
establish a pH of 
water to make 1 l 1 l 
______________________________________ 
Table 4 summarizes the sensitometric results and dot quality ratings at 
different development times at 32.degree. C. 
TABLE 4 
______________________________________ 
Sol. dev. time 
fog S grad(t) 
grad dot rating 
______________________________________ 
C 20 s 0.05 91 6.2 20 1.5 
C 40 s 0.08 105 8.1 32 1.5 
C 60 s 0.10 115 9.3 27 1.5 
D 60 s 0.03 72 4.5 -- 3.5 
D 90 s 0.04 93 4.8 14 3-3.5 
D 120 s 0.06 91 4.6 17 3-3.5 
______________________________________ 
Table 4 clearly illustrates the better gradations and dot quality ratings 
reached at shorter developing times by means of the developer according 
tot he invention compared to Zwicky's formula. 
EXAMPLE 3 
Samples of the same graphic arts material as in example 1 were exposed in 
the same way and developed at 32.degree. C. in developers (E) and (F) 
differing only in pH value with a composition represented in table 5: 
TABLE 5 
______________________________________ 
ingredient solution E solution F 
______________________________________ 
sodium iso-ascorbate.H.sub.2 O 
184 g = 
potassium bromide 25 g = 
1-phenyl-5-mercaptotetrazole 
0.08 g = 
potassium hydroxide to 
11.75 12.35 
establish a pH of 
water to make 1 l = 
______________________________________ 
The sensitometric results and the dot quality ratings are summarized in 
table 6: 
TABLE 6 
______________________________________ 
Sol. dev. time 
fog S grad(t) 
grad dot rating 
______________________________________ 
E 20 s 0.03 83 4.1 9.3 3 
E 30 s 0.03 93 4.7 11 2.5 
E 40 s 0.03 98 4.4 13 2.5 
E 50 s 0.03 100 4.5 18 2.5 
E 60 s 0.03 102 4.6 21 2.5 
F 20 s 0.03 98 6.0 9.5 2 
F 30 s 0.04 129 8.4 24 1.5 
F 40 s 0.04 135 9.0 40 1.0 
F 50 s 0.05 138 9.8 42 1.0 
F 60 s 0.05 145 9.6 48 1.0 
______________________________________ 
The results presented in table 6 illustrate clearly the favourable 
influence of a pH higher than 12 according to the invention on the 
gradation and dot quality rating. At the same time this example 
illustrates the usefullness of iso-ascorbate as an alternative developing 
agent. 
EXAMPLE 4 
The same graphic arts material as in previous examples was again exposed in 
the same way and developed for 20 seconds at 32.degree. C. in developers 
(G), (H) and (I) differing only in pH value with a composition represented 
in table 7: 
TABLE 7 
______________________________________ 
ingredient sol. G sol. H 
sol. I 
______________________________________ 
ascorbic acid 110 g = = 
potassium bromide 25 g = = 
1-phenyl-mercaptotetrazole 
0.08 g = = 
sodium hydroxide to 
11.5 12.0 13.0 
establish a pH of 
water to make 1 l = = 
______________________________________ 
The sensitometric results and dot ratings are summarized in table 8. 
TABLE 8 
______________________________________ 
Sol. pH fog S grad(t) 
grad dot rating 
______________________________________ 
G 11.5 0.04 79 3.4 --.sup.(1) 
4 
H 12.0 0.04 105 3.9 15 3 
I 13.0 0.12 138 9.4 16 1.5 
______________________________________ 
Note: .sup.(1) density 3.0 was not reached. 
This example like the previous one illustrates the effect of pH on the 
gradation and dot rating. 
EXAMPLE 5 
A series of developing solutions varying only in ascorbic acid 
concentration were prepared (see table 9); the rest of the composition was 
the same as in solution (H) of example 4 (pH=12.0). 
TABLE 9 
______________________________________ 
solution conc. ascorbic acid 
______________________________________ 
J 20 g/l 
K 35 g/l 
L 71 g/l 
M 110 g/l 
N 150 g/l 
______________________________________ 
The same graphic arts material as in the previous examples was exposed in 
the same way and developed for 40 seconds at 35.degree. C. with solutions 
(J) to (N). Table 10 summarizes the sensitometric results and the dot 
quality ratings. 
TABLE 10 
______________________________________ 
Sol. fog S grad(t) grad dot rating 
______________________________________ 
J 0.03 -- 2.7 -- 5 
K 0.03 -- 3.4 &gt;4 
L 0.04 112 4.7 16 3 
M 0.04 112 5.1 20 3 
N 0.16 126 8.2 21 2.5 
______________________________________ 
The results illustrate clearly the effect of an increasing concentration of 
ascorbic acid on the gradation and dot quality rating. At pH 12.0 which is 
the minimal value according to of the present invention a concentration of 
more than 70 g/l ascorbic acid corresponding to 0.4 mole/l was needed to 
obtain an acceptable result.