US1591499A - Process of changing the light sensitiveness of photographic emulsions and intermediate used therein - Google Patents

Description

- sensitizing substances Patented July 6,

UNITED .s'r

res PATENT-OFFICE.

.QAIUEL E. SHEPPARD, OF ROCHESTER,

CQRPORATION 0! NEW YORK.

rnoczss or cnaueme THE LIGHT snnsrrrvnn'nss or rno'roewmc nuunsrons am) mrnmmnwra use]: 'nmnnm.

11o Drawing.

This invention relates'to processes for changing the light sensitiveness of hotographic emulsions. vention is. to provide a process by means of which photographic emulsions ma be improved as regards their light-sensitiveness, without impairing the other properties of the emulsion. Another object ofthe invention is to provide-a process in which a potential sensitizer may be incorporated with the materials of the emulsion, and then the sensitizer liberated at the desired .time in the emulsion-making process. Other objects will hereinafter appear.

Inmy prior application 718,410, filed June 6, 1924, for art of light sensitive photographic materials, I have shown that light may be prepared by suitably extracting certain organic materials. When these substances are incorpo-' rated in photographic emulsions, such as those ofthe gelatino-silver-halid type, theygreatly ;:.increase the light-sensitiveness of such emulsions.

I have now. found that such sensitizing materials may be prepared in a latent form in which they do'not have a sensitizin action, and then can be readily changed rom such form so that they do have the sensitizing action. I have 7 they stay in their latent form, when incorporated with the materials of the emulsions, and may be'converted into the active sensitizing form in such emulsions at the desired time.

In the preferred form of my invention the sensitizing substance is combined with larly in the case of glucosides, by using a an organic group or radical which maintains it in its latent stateuntil it is released from such group or radical. For instance, a mustard oil sensitizer may be combined in a gluoside, in which form it is latent or inac tive, as regards sensitizing action.

- While the sensitizing substance may be released from the group or radical by different chemical steps, I prefer to do it, particu hydrolyzing enzyme. I shall now describe one form of my invention by way of illustration, but it will be understood that the invention is not restricted to the details'thus given, except as indicated in the appended claims. Since mustard oils and their gluco-' -One object of t e in- 'glucosides,

different cells,

further discovered thatv lpplieationflled December 2, 1925. Serial No. 72,811.

sides are readily prepared and easily treated, I- shall refer to them by way of example.

Sensitizing mustard oils are contained in combined or latent form in vegetable bodies, particularly in the seeds of the plants of the order cruciferae. They occur usually asthe monosegroup or radical with which the oil is combined acting to prevent light-sensitizing action.

While these glueosides can be hydrolyzed in various ways, I have found it particu-' .larly convenient to hydrolyze them b means of enzymes. The latter can be use in the emulsion itself, without adversely afi'ecting the latter. Moreover suitable enzymes-occur in the same plants as the glucosides only in and can be obtained in suit. able form by simpletechnique.

I may, for example, crush the seeds of black mustard (Brasswa n/igra) and macerate them in hot'alcohol (pure natured) which is raised to a boiling point and held at this point for some time. The residue is thenextracted with cold water and evaporated down to a relatively small volume. This watery extract is then made slightly acid by the addition of tartaric acid. The liquid'is then still further evaporated and extracted with alcohol. The syrup thus obtained is best diluted and neutralized with potassium carbonate in order to prevent decom osition.

T e syrup in this form constitutes a latent sensitizer because it contains the sensiethyl or detizing substance, namely the allyl mustard I New Your, nssrenon 'ro EASTMAN KODAK comrm, or nocrms'rnn, NEW max, A"

halid emulsion of the kind described in my above cited prior ap ication, it produces no sensitizing efiect. ut at the same t1me 'itproduces no ill effects on the other propertles of the emulsion: It can be thus incorporated atany of the stages in the prepara-' tion of the emulsion, even-the preliminary ones, say in the gelatine for instance.

Finally the emulsion, containing the latent sensitizer, can be greatly speeded up or sensitized by liberating the combined mustard oil, such as allyl isothiocyanate, which is contained in'it. This liberation can be done by melting the emulsion, at a temperature preferably under 50 0., and adding to ment of the sensitizing operation "be carried so far as to coat the emulsion on it a relatively-small amount of gelatine containing the enzyme or ferment. Postponemay even its support while it still contains the latent sensitizer, and then overcoat the emulsion with gelatine containing the enzyme. The latter diti'uses into the emulsion and liberates the scusitizer, thereby greatly increasing the light sensitiveness.

The enzyme or ferment may be prepared in any preferred way. I may, for example, macerate white mustard seeds (Si/mp5s 017m) and extract them with cold water, the extract being evaporated in a vacuum below 40 C. until a syrup is obtained. It is desirable to keep the temperature below that specified, in order to prevent the destruction of the enzyme by heat. Upon adding alcohol to the syrup the enzyme is precipitated out. This alcoholic precipitate keeps its activity for a considerable time, it it is not exposed to too high a temperature or other protein coagulating agents. Tt may be incorporated in gelatine.-and then the mixture utilized to activate the latent sensitiz'er in the emulsion,

as described hereinabove.

\Vhenthe latent sensitizer, such as a glucoside of an isothiocyanat-e, is incorporated in a colloid, such as gelat-ine, before thecolloid is made into an emulsion, the product constitutes a valuable and convenient inter mediate in the process of making photographic emulsions, particularly silver-halid ones.

The proportion of latent sensitizer can vary: but in the emulsions and in the interniediates it is used in quantities whichwill yield the amounts of active scnsitizcr indicated in my hereinabovc cited application. Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

1. The process of changing the light-sensitiveness of a photographic emulsion which comprises incorporating in said emulsionan organic compound in which asensitizing substance is'combined with a group which renders it latent, and. thereafter releasing saidsubstance in active form from said compound.

2. The process of increasing the lightsensltiveness of a c0ll01ds1lver-salt emulsion which comprises incorporating in said emul-' step of incorporating in said emulsion an organic latent sensitizer.

5. In the process of preparing a colloidsilver-halid emulsion the steps of incor porating with the ingredients of said emulsion a latent sensitizer capable of being activated by an enzyme, and incorporating an enzyme in said emulsion to activate said sen sitizer. 6. In the process of preparing light-sensitive colloid-silvcr-halid emulsions the steps of incorporating with the ingredients of said emulsions a latent scnsitizer capable of being activated by an enzyme, mixing an enzyme with a colloid, and incorporating said mixture of colloid and enzyme into said emulsion to activate said sensitizer.

7. As an intermediate in the manufacture of colloid-silver-halid emulsions, a colloid having distributed therein particles of silver-halid and a latent organic sensitizer.

3. As an intermediate in the manufacture of gelatino-silver-halid emulsions, gelatine having distributed therein minute particles of silver-halid and a sensitizing compound kept in latent term by combination with an organlc group.

9. An intermediate in the manufacture of gelatinosilver-halid emulsions comprising gelatine having distributed therein minute particles of silver-halid and a latent sensi' tizer comprising a compound from which mustard oil can be released by means of an enzyme.

Signed at Rochester, New York, this 25th day of November 1925.

SAMUEL E. SHEPPARD.