US 2377375 A
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June 5, 1945. H. D. RUSSELL 2,377,375
I THIOSALICYLIC ACID ANTIFOGGANT Filed Dec. 14, 1943 EMULSION CONTAINING THIOSALICYL/C ACID I0 V// /j/ SUPPORT 13 OVERCOAT CONTAIN/N6 TH/OSAL/CYLIC. ACID BACK/N6 CONTAINING TH/OSflL/CYL/C ACID HAROLD D. RUSSELL IN V EN TOR W W MQAQA A TTORNE YS Patented June 8, 1945 Harold D. Russell, Rochester, N. 1., Eastman Kodak Company, Roch to a lign 01 ester, N. Y.,
corporation of New Jersey Application December 14, 1943, Serial No. 514,242
This invention relates to photography and particularly to a method of preventing fog in photographic silver halide emulsions.
One of the problems met in the development of photographic emulsions for protracted periods of time or at higher temperatures than normal is that of fog. A more or less uniform veil of silver, which is known as fog, is produced in the emulsion when the limits of time and temperature of development are exceeded.
It is, therefore, an object of the present invention to provide a method for reducing fog in photographic emulsions. A further object is to provide a photographic emulsion containing a novel fog inhibiting agent. A still further object is to provide a photographic developing solution which has decreased tendency to produce fog in a photographic emulsion. Other objects will appear from the following description of my invention.
These objects are accomplished, according to my invention, by incorporating thiosalicyclic acid in a photographic emulsion, developer, backing or overcoating layer.
In the accompanying drawing. Fig. 1 is a sectional view of a photographic film having an emulsion layer containing thiosalicylic acid, Fig. 2 is a sectional view of a film having an overcoating layer containing thiosalicylic acid and Fig. 3 is a sectional view of a film having a backing layer containing thiosalicylic acid.
When used in the developing solution, the thiosalicylic acid may be employed as the free acid or as the sodium salt or other water-soluble salt. The amounts used may vary from .01 gram to 1 gram per liter of developer. The compounds may also be used in a prebath prior to development.
When used in the emulsion itself, the thiosalicylic acid may also be employed in the salt form and may be incorporated at any stage in the manufacture of the emulsion. The amounts used in the emulsion vary from 0.2 mg. to 20 mgs. per 50 grams of silver halide.
My invention will be further illustrated by reference to the following examples:
7 Example 1 The following example illustrates a developing solution containing thiosalicylic acid.
Monomethyl-p-aminophenol sul- Water to .lite 1 Example 2 The following example illustrates a developing formula which produces high contrast:
lh'droquinone ..grams-- 15 Sodium sulfite (desiccated) do Sodium carbonate (desiccated) ..-do 50 Potassium bromide do 10 Thiosalicylic a i do 0.1 Waterto liter 1 Example 3 therefore avoids the tendency to produce variations in the sensitometric characteristics of the emulsion. When thiosalicylic acid is applied in a gelatin layer over a silver halide emulsion layer, for example, the rate of growth" of fog with development time may be reduced without substantially changing the sensitometric curve shape or the maximum density of the emulsion.
The thiosalicylic acid may be used alone as an antifoggant or it may be combined with another antifoggant which may be present either in the same layer as the thios'alicylic acid or in an adjacent layer.
In the accompanying drawing I have shown in Fig. 1 a sectional view .of a photographic film comprising a support iii of any suitable material such as glass, cellulose ester, synthetic resin or paper, having thereon an emulsion layer H containing thiosalicylic acid. Fig. 2 shows a similar material in which the support l0 has thereon a gelatino-silver halide emulsion layer I2 which is overcoated with a gelatin layer l3 containing thiosalicylic acid. Fig. 3 illustrates a further modification in which the support i0 is coated with an emulsion layer I2 and the opposite side of the support i0 has thereon a gelatin backing layer It containing thiosalicylic acid. The thinsalicylic acid present in a backing layer is dissolvel in the developer upon development and exerts its antifoggant action during development.
It will be understood that the examples and modifications included herein are illustrative only and that my invention is to be taken as limited only by the scope of the appended claims.
1. The method of reducing fog in a photographic silver halldeemulsion, which comprises exposing said emulsion and developing it in the prising a silver halide developing agent and a tog-inhibiting amount of thiosalicylic acid.
6. A photographic element comprising a support having thereon a silver halide emulsion layer and another layer containing a tog-inhibiting amount of thiosalicylic acid.
7. A photographic element comprising a support having thereon a silver halide emulsion layer and a gelatin overcoating layer containing a 10 fog-inhibiting amount of thiosallcylic acid.
HAROLD D. RUSSELL.