US2374921A - Photographic developer - Google Patents

Description

. ing a coarse, grainy structure.

Patented May 1, 1945 UNITED STATES PATENT OFFICE PHOTOGRAPH IC DEVELOPER Albert L. Bunting, Dearborn Mich assignor, by mesne assignments, to E. J. Gray and Arthur M. Smitlnboth of Detroit, Mich trustees No Drawing. Application August 18, 1941,

a Serial No. 407,357

4 Claims.

ments Prior developers producing relatively small aggregates or clusters of silver particles for the purpose of reducing the appearace of graininess require notoriously long development times. The use of such developers frequently results in the production of fiat negative, that is, negative lacking contrast, and in manyinstance lacking good detail, especially shadow detail.

Consequently, no former developer has been wholly satisfactory, especially for use with small negatives, such for example as 35 millimeter negatives. Since enlargements are customarily made -from these small negatives, they must possess good detail and be as free as possible from the appearance of graininess and must possess suitable, preferably long-scale, contrast and detail as all defects are accentuated in enlargements made therefrom.

Developers intended and adapted to produce images having the desired contrast and detail can do so only by producing images containing relatively large aggregates or clusters of silver particles and thus give the appearance of hav- So-called fine grain or fultra fine grain" developers hereto fore used, while more or less eilective in reducing the sizes of the clusters or agglomerates of the silver particles, are not wholly satisfactory for they produce negatives which usually are lacking in the desired detail and contrast, and

they require an excessively long development time.

, It is, therefore, one object of the present invention to provide a photographic developer adapted to produce a print or negative having little or no formation of clusters or agglomerates of the silver particles so that the photographic image developed therein is free from. the appearance of coarseness or graininess. the present developer being also adapted to produce 'a photographic image possessing the desired properties of sharpness. contrast and detail, especially shadow detail.

It is another object of the invention to provide a photographic developer which is adapted to produce a clean print or negative free from any over-all deposit of silver or any other substance darkening its appearance and rendering its image indistinct or muddy, as such prints and negatives are often termed. Accordingly, the present developer produces a negative or print not only free from the appearance of grain,

but also possessing clear or white highlights,

dark or black shadows, and distinctly differentiated intermediate gradations, which result in producing an image having good detail and contrast.

Another object of the invention is to provide a so-ca1ledflne grain" photographic developer having a short development time, said developer being comparable in this respect to the faster acting of the present coarse grain developers, and having less than half the development time of conventional commercial so-called fine grain or ultra fine grain developers.

Still another object of the invention is to provide a photographic developer of the foregoing general character in which the ingredients may be predetermined or controlled to increase or decrease the development time, to increase or decrease the ability of the developer to produce contrasts in the negatives or prints, and to produce agglonierates or clusters of silver particles of a minimum size.

A further object of the invention is to provide a developer which may be used with panchromatic film or other film sensitive in the wave length span of light ordinarily employed in darkrooms, but which will permit inspection of said film in said light, after a very short development interval, without fogging or other undesirable results.

Still a further object of the invention is to provide a photographic developer which is stable at room temperature ranges for a relatively long period of time even when exposed to the air, andwhich is adaptedto be used satisfactorily over a wider temperature range than other known developers, the present developer being adapted to produce equally good results at all points within its temperature range, and if used repeatedly at or about any given point in said temperature range it will produce consistently duplicative results.

Other objects and advantages of the present invention will become apparent during the course of the following description and of the appended claims forminga part hereof.

Generally speaking, a photographic developer embodying the present invention is a chemical ever, generally speaking, amounts o' f l these' Wetting agents are all that is compound or admixture of chemical compounds containing one or more of the following types of compounds or substances:

(1) A wetting agent adapted to cause adhesion or afllnity between the aqueous solution of the present developer and the photographic emulsion to be developed. In particular, this wetting agent aids in causing the developer to permeate or penetrate the pores" of the photographic emulsion and thus facilitates the reaction between the silver compound carried in the emulsion and the. developing materials to be employed.

(2) A buffing agent adapted to maintain the solution as a substantially neutral solution.

(3) An anti-fogging agent adapted to prevent undesired precipitation of the silver or other image-forming compound uniformly over the emulsion. Such precipitation causes darkening of the image or may destroy it by what is known as "chemical fogging." (4) A reducing agent adapted to reduce the light-struck -or photo-sensitized silver compound to metallic silver, or to reduce the lightsensitive compound in the emulsion to the imageforming substance.

(5) A preservative which is also preferably a mild reducing agent, thereby aiding in the reducing action of the developer.

To the foregoing ingredients there maybe add! ed, if desired,- an inhibitor for slowing down the developing time of the developer. This .is recommended only if it is particularly desirable to secure an image having very small aggregates or clusters of silver particles-which will result from a slower development.

It is to be understood, as hereinafter set forth, that the present developer does not necessarily contain an ingredient selected from each one of the aforesaid classes of compounds or substances.

Tm: War'rmo AGENT The wetting agent should be selected from the group of water-soluble or water-dispensable stood that other wetting agents are also satls factory. For example, the oleates, stearates orpalmitates of triethanolamine also may be used, as may the polyhydric alcohols.

The amount of wetting agent employed, will depend upon the particular agent selected. Howrelatively small required. In general, the known proportions necessary for.'use in an aqueous solution-may be used. For "example, if the various dicarboxylic" acids are employed, it has been found that a .12 to-.-2--percentgsolution produces good results, that is,:1.2 grams-i202 grams of the dicarboxylic acid per liter of .the present solution comprises the preferred range of proportions. 'It will be understood, however, that this range is but a preferred range, and more or less of the wetting agent may be employed if particular results are desired. although the foregoing proportions have been found satisfactory for normal use.

While it is preferable to utilize a wetting agent, the present developer can be made up without any such agent. However, if it is made up the latter way, the development time is increased materially, but satisfactory photographic images can be produced under these circumstances.

THE Burraamc AGENT As the buflering agent, any suitable buffer may be employed which will maintain the solution approximately neutral or somewhat alkaline, that is, neither strongly alkaline not strongly acidic. For this purpose it is recommended that dibasic sodium borate be employed. This compound has been found to be an admirable buil'ering agent, and is effective since a solution containing this salt possesses a very nearly constant pH of approximately 7.5.

It will be understood, however, that while dibasic sodium borate comprises a preferred bufferlng agent, other buffering agents may be used. For example, borax (NazBlo-l) may be employed.

While the developer containing a buffering agent, as explained above, is distinctly preferable, a buffering agent may be dispensed with entirely. However, if the bufferin agent is dispensed with, it is recommended that the concentration of sodium sulfite (another one of the ingredients of the present developer explained hereinafter) be kept at or near its maximum concentration. Also, if this buffer is not utilized, the wetting agent explained hereinbefore should be utilized. In other words, it is preferable that the developer contain both the wetting agent and the buffering agent. If either agent is omitted, it is desirable that the other agent be used.

The concentration of the buffering agent will, ofcourse, depend to a large extent upon the particular compound selected. A skilled chemist can determine how much of the buffering agent is needed in a particular solution to maintain the solution at or near a pH of 7 to 7.5. If dibasic sodium borate is employed as the buffering agent, it is recommended that approximately 11 grams ofthis compound per liter of developer be employed. However, this concentration does not appear to be critical and may be reduced to approximately 4 grams per liter and may be increased to about 20 grams per liter. understood that this range of proportions is merely recommended .in view of applicant's experience with the buffering agent, and it is contemplated that, for particular purposes, the concentration thereof may be further increased or decreased.

Trill ANTI-FOGGING Aosn'r Another of the ingredients utilized in the pres-- in what is known as chemical fogging and ruin the negative or print. If such precipitation takes place but slightly, the print will be darkened somewhat and will suffer accordingly, especially through loss of detail and lack of contrast, although the image may be visible. Therefore, it is preferable to prevent any such precipitation.

It isto be However, if a very flat print (one not having much contrast and in which the detail is relatively unimportant) is desired, the present anti-fogging agent may be eliminated. However, as stated, for most purposes detail is desired, as is at least a certain amount of contrast; thus, the use of said agent is usually desirable.

I have found that any solublebromide which will not react to form insoluble compounds may be utilized as an anti-fogging agent. In particular, ammonium bromide (NHqBr) is recommended, although it tends to e acid in nature. If the aforementioned buffering agent is employed, the solution will retain its pH value despite this characteristic of the ammonium bromide. Also, sodium or potassium bromide (NaBr or KBr) may be utilized isdesired.

I have found that approximately 1 gram per liter of ammonium bromide produces satisfactory results, although it appears that from gram to as much as grams may be employed if desired. However,-the practical limits appear to be from be understood that the developer musttontain a reducing agent.

V; gram, below which the compound appears to be used up, up to approximately 5 grams. If a concentration of over 5 grams per liter is em I ployed, the developer tends to produce a very contrasty print or negative, that is, one having completely clear highlights an'lvery dark backgrounds with very few gradations between the two. Where such contrast is sought, as in lan- 1 tern slide development or half tone and line work,

- it may be desirable to use a relatively high concentration of the above-mentioned bromide. However, for normal development where such very high contrasts are not particularly desirable, the bromide concentration should not exceed approximately 5 grams per liter.

Tm: DEVELOPING AGENT lized in photographic developers may be employed. For example, I have iound that a mix-, ture of hydroquinone and monomethyl para amino phenolsulfate produces satisfactory results. The latter compc nd is known commercially as Elon or Metol and is sold under such names by the Eastman Kodak Company. I have found that from /2 to 3 grams of Elon per liter of devel oper produces a satisfactory result when used with 1 to 12 grams of hydrorminone per liter. It is to be understood that any amount of either of these substances within the foregoing ranges, or any combination thereof, may be employed, Also, it is to be understood that one may be employed alone if desired. However, Elon," if used alone, tends to produce avery soft or flat negative print having little detail of, contrast, while hydroquinone, if used alone, tends to produce a very brilliant contrasty print. Thus, a mixture of the out rnaterially affecting the characteristics of the two appears to be more suitable and more desir- Tm: PRESERVATIVE Another one" of the ingredients utilized in the present developer is a suitable preservative. Naturally this preservative is utilized chiefly to extend the life period of the developer after it has been made up, and it need not be added if the developer is to be used shortly after its preparation. Its'use is-recommended, however, since for some reason not now known to me, the use of the preservative appears to improve the results obtained from the use of the developer.

A suitable preservative is sodium sulfite', which is also a mild reducing agent and thereby app.ars to aid. the hydroquinone and "Elon in effecting the reduction of the light-struck or photo-sensitized compounds inth'e emulsion.

The amount of sodium sulfite employed may vary widely, although it is recommended that a relatively large amount be employed. I, therefore, recommend that approximately grams per liter be used, inasmuch as this concentration appears to render the present developer particularly stable and does not appear to affect deleteriously the quality of the images. Sodium sulfite may be employed up to the saturation point of the solution, which'is approximately 200 grams per liter. On the other hand, the concentration of this ingredient may be decreased considerably and may be as low as 20 grams per liter with effective results. As pointed out above, the principal purpose of the sodium sulfite is as a preservative and, therefore, still smaller amounts may be utilized or it may be dispensed with withpresent developer.

SUBSTANCES roa PRODUCING AN ESPECIALLY FINE Guam In addition to the foregoing ingredients, the present developer may include substances adapted to produce especially small silver particles or agglomerates thereby providing a print or negative which may be considerably enlarged without showing any grain. Beta naphthol has been found satisfactory for this purpose although it considerably lengthens the development time. When but 2 gram of beta naphthol per liter is employed, it has been found to approximately double the development time. While normally this lengthening ofthe development time would not be desirable, it appears to be helpful in producing even the smaller aggregates or agglomerates of the silver particles. Therefore, I have found that the use of the presently disclosed additional substances does produce the finer aggregates or agglomerates, although a generally comparable result may be attained without its use. As explained above, I recommend that V: gram per liter of beta naphthol be employed, although this amount may be increased to approximately 5 grams per liter.

Alpha naphthol, phenol, and naphthol sulfonic acids may be employed instead of beta naphthol if desired. Also, any suitable compound intended to slow down the reducing activity of the reducing agent may be employed provided that it does not have deleterious side reactions.

INSPECTION DURING DEVELOPMENT If. desired, another ingredient which may be added tothe present developer is an agent for or similar film during development thereof. Normally films of this character would be sensitive to such light, and therefore could not be inspected during development if conventional de- Potassium, sodiu The foregoing example of the present developer was found to have, a developing time of about 6 to 7 minutes atapproximately 21 C. when used on "Agra Finopan film. This film was developed to approximately .8 gamma. Under like circumstances and conditions, the aforesaid developer was found to have a development time of from 6 to 7 minutes when used on "Agfa Supreme" film. The development, time was approximately 6.5 minutes forEastman Panatomic" film; about velopers were employed, for they would fog. minutes for "duPont Superior film; and about The desirability of frequent visual inspection of 75 seconds for Eastman" positive film. such films during development is well known. In order to develop these films to a compa- For example, pinakryptol green may be added in rable extent, that is, to approximately .8 gamma, amounts of approximately A: gram per liter of the so-called "fine grain or ultra fine grain" dedeveloper, although this amount maybe re- 10 velopers now available on the market require ed or in r s mewh and m y be used from about 40 minutes to 60 minutes. Among, in quantities a low a 25 gram per liter. If such developers are Eastman DK-20, Champlin this compound is added, a normal panchromatic No. and Edwal No. 12. film or the like may be inspected with a Wratton In addition to having much faster development 8: Wa nwri ht 0- fi ter disposed o a 6 time than the aforesaid presently available fine dinary lamp after approximately 1 minute of grain developers, the present developer was development. The light may be fairly bright; found toproduce an image at least comparable in also a relatively bright gre n light may be emfineness if not superior thereto. In addition, the p y present developer produced negatives having Another ingredient suitable for this purpose is much better detail than those produced by the p kryptol yellow which h he same general aforesaid developers, especially shadow detail, efiect as plnakryptol green. Also, phenosafranine and produced much sharper, clearer images. may be employed in amounts of approximately Accordingly, the present developer appears to /2 gram per liter, and renders the aforesaid film be an improvement over present developers since suitable to be inspected with the usual dull green it not only produces more satisfactory results, darkroom safe lights after approximately 1 minbut does so in a much quicker time and is thereute of development. fore much more practical and convenient to use.

I claim: CLEARING THE PRINT 0R NEGATIVE 1. A photographic developer containing a wet- If the present developer is e p P ting agent. a buffer adapted to maintain the soducmg a hunt negatlve' I have found that lution neither strongly acidic nor strongly alkathe required for c ring the print or negaline, a water-soluble bromide, a developing agent, tive after development is greatly reduced. Apa preservative and anaphthol sulf m m parently sufiicient wetting agent is retained in 2' A photographic developer comprising an the emulsloh layer of the Print negative to aqueous solution containing a dicarboxylic acid accelerate the penetration of the clearing agent wetting agent, dibasic Sodium bomte', a developin the pores of the emulsion. This more rapid m agent, and beta naphthoL penetration enables said clearing agent to react 3. A photographic developer comprising an with or dissolve the products in the emulsion other aqueous Solution containing a dicm-boxync acid than the developed silver, thereby producing a 40 wetting t, dibasic sodium borate, a t cleared print. For instance, a solution of "hypo" soluble bromide, hydroquinone, monomethyl para (sodium thiosulfate or the like) may be employed m phenolsmfate and beta naphthol.

as the clearing agent, and for the-reasons set 4. A photog p c developer adapted to proforth abo will clear thepr t more rapidlyr'if duce a rapid development of a photographic the P e e t deve ope is usedimage with the production of .very small agglomerates or aggregates of the light-struck photoshgclnc DEVELOPER sensitive material, while preserving detail and a Although I have explained. my ihventlon in desired scale of contrast, said developer compristail, the following general formula and specific mg a aqueous solution containing a wetting example a given by Way further explanation agent selected from the group consisting of diahd not of hmitatmni carboxylic acid wetting agents and the oleates,

General formula i%i.%t,ifant;ai;::::::::::::::::: 28353: i ..?.'t.;$%?*5% ;f

m or ammonium bromide--. Approx. gms. to approx. 25 gms.

A Dicarboxylic acid Approx. 1.2 gms. to approx. 2 gms, ggig l I 31 1 500? in gm.tto approx. 3 gms. water Tg inak e oiliit r iiiiitfin Spec fi example stearates, and palmitates of triethanolamine, a I Gms. buflfering agent selected from the group consist- Elonf Approx. 1.75 ing of dibasic sodium borate, borax, sodium carsodium sulflte Approx. bonate and sodium bicarbonate, an anti-fogging Dibasic sodium borate e Approx. 6.5 0 agent selected from the group consisting of am- Potassium bromide Approx. .5 monium, sodium and potassium bromides, a de- Aerosal O. T." Approx. 2.0 veloping agent comprising a mixtiire of hydro- Hydroquinone Approx. 2.0 quinone and monomethyl para amino phenolsul- Water To make one liter of solution fate, a preservative comprising sodium sulfite, an

inhibitor selected from the group consisting of alpha and beta naphthol, phenol and naphthol sulfonic acids, and a dye' selected from the group consisting of pinakryptol green, pinakryptol yellow and phenosafranine.

ALBERT L. HUNTING.