US2321348A - Photographic developer - Google Patents

Description

Patented June a, 1943 PHOTOGRAPHIC DEVELOPER James Reid Alburger, Mei-ion, Pa., assignor to Radio Corporation of America, a corporation of Delaware I No Drawing.

Claims.

This invention relates to an improved photographic developer and, more particularly, to a developer which will produce surface development Application January 2, 1940, Serial No. 312,094

ancing of the alkali by alum serves to maintain the alkalinity constant, since aluminum hydroxide is precipitated and. alkali is released as the and relatively low contrast. For some purposes,

particularly where high definition is required, it is desirable that the image in the photographic emulsion-shall be developed inwardly from the surface rather than through the entire depth of the emulsion at the same time. When this is done, diffusion of the image in the emulsion has a minimum effect, since the degree of development can' be chosen to give the best balance between 'density and diffusion. If a developer is used which develops the image uniformly through the thickness of the emulsion, the diffused image is developed along with the rest of the image and such control can not be secured. While there are a few developing agents which tend in an ordinary developing solution to give development which is predominantly from the surface, this does not apply to the ordinary developing agents as used in the usual developing formulas.

I have discovered, however, that if the ordinary developing agents are used with an extremely high concentration of alkali, the development can be caused to occur predominantly from the sur-" face, with the relative amount of surface development depending on the alkali concentration.

With ordinary developer formulas, it is impossible to use 'an alkali greater than about 50 grams of sodium hydroxide per liter, or the equivalent, due to the extreme softening effect of the alkali on the gelatine. I have avoided this result however, by balancing the alkali content with alum, as described and claimed in my application Serial No.

205,363, filed April 20, 1939, now Patent N0.

' 2,199,904, issued May 7, 1940. As described in the said patent (page 3,1ines 55, et seq.) if the sodium hydroxide or other alkali is added to the solution first it may be balanced with alum by adding alum to the solution until no more will dissolve thereby saturating the solution with alum. Conversely, if the amount of alum to be used is known, the alum may be dissolved first and the alkali in thesolution is used up or neutralized.

The main object of the invention is to providean improved photographic developer.

Another object of the invention is to provide a photographic developer which will give. a predominantly surface development.

Another object of the invention is to provide a photographic developer which will have a high alkalinity but give an image of low contrast.

In my aforesaid Patent No. 2,199,904, issued May 7, 1940, I have described and claimed a developer of substantially the following formula:

This developer will give for a certain film, such, for example, as duPont 100, a gamma of 1.2 for a two-minute development at approximately 70 F. If, however, the alkali content of the developer is increased and is kept balanced with alum by maintaining the ratio of approximately 3 parts of sodium hydroxide 1504 parts of alum, I find that there is a point at about 100 grams per liter of sodium hydroxide where the image noticeably changes its character. Instead of the image developing substantially uniformly through the thickness of the emulsion, it develops predominantiy from the surface, and the amount of this surface efiect increases with the alkalinity up to alkaline hydroxide added later until the initial precipitate of alum hydroxide is just redissolved. If the proper proportions of both materials are once determined in this manner, they may both be added at the same time.

The hardening effect of the alum prevents excessive softening of the gelatine by the alkali and thereby permits the use of alkali concentra, tions much higherthan could be used in other developer formulas. At the same time, the ital-T approximately 240 -'grams of sodium hydroxide per liter of water. not only does the surface effect increase but the contrast decreases. For example, with a developer having the following. formula:

Hydroquinone 15 Sulfite 30 NaOH -240 KBr v 9 Alum a 320 Water 1000 the gamma for a two-minute development with duPont No. film, the same typereferred to above, falls to .62. v

The high alkali concentration seems to alter the penetrating effect of the developing agent. This result may be due to polymerization of the If the alkali content increases,

developing agent, it may be that the hardening eilect oi. the alum on the gelatine plus the water aflinity or the alkali decreases the tendency for the solution to penetrate the gelatine, or it may be a combination oibotheflects. Whatever the cause,vthe developing agent acts first on the portion of the image at the surface and then gradually airects the deeper portions or the image.

The same effect applies in other developing agents which operate in alkaline solution. A

I claim as my invention:

1. A photographic developer containing a developing agent, more than 100 grams of caustic alkali per liter of solution and alum to saturation;

2. A photographic developer containing hydroquinone, more than 100 grams of caustic alkali per liter of solution and alum to saturation.

4. A photographic developer containing a developing agent, a quantity oi! caustic alkali of the order or 240 grams per liter of solution and alum to saturation.

5. A photographic developer containing hydroquinone, caustic alkali of the order of 240 grams per liter of solution and alum to saturation.

' JAMES REID ALBURGER.