US2199580A - Photographic printing - Google Patents

Description

Patented May 7, 1940 UNITED STATES PIFOTOGRAPHIC PRINTING Mayson 1!. Tucker, New york, N. Y.

Application September 10, 1938, Serial No. 229,325

No Drawing.

This invention relates to photographic printing and has for its principalobject to provide an improved photographic printing paper capable of being printed upon in halftones, developed and fixed in white light; The invention also provides a method for carrying out photographic printing operations in white light and a method for preparing the paper of the invention.

In contact printing of photographs in half 10 tones from picture negatives it has heretofore been practically necessary to develop and fix the exposed print in the dark, or at least in a dim light substantially free from actinic rays. While this disadvantage to heretofore known methods of photographic printing is of no particular consequence to professional photographers, it is of considerable consequence to amateurs'who find' it dimcult to provide the necessary dark-room facilities.

Various attempts have been made to develop methods to make it possible to print photographically, in ordinary white light, but such attempts have not proven particularly successful. It has been proposed, for example, to incorporate a colord dye (such as phenolphthalein) in the solutions employed for development and fixing of the photographic image after exposure or the printing paper, but this expedient still requires that the paper be mounted inthe printing frame and so that the exposed paper he transferred from the printing frame to the developer and from the developer to the fixing solution in the dark-room.

Such procedure thus eliminates the need for av dark-room only during those phases of the print ing operation when the printer has little need for.

500 foot-candles or more), such as the light within a fraction of an inch of the bulb of a common 60 watt electric lamp of the so-called 50 Mazda type, and may be subsequently developed and fixed in ordinary indoor light without fogging.

The paper of the invention comprises a paper backing coated with a standard well-known pho- 55 to-sensitlve emulsion applied to a surface there- 'of and having a colored dye applied as a separate film over the exposed surface 0! the sensitive emulsion. r w The colored dye as it is employed on the film is ofsuch character as to be substantiallyopaque 5 to the actinic rays of ordinary subdued daylight.

or artificial white light of brightness of the order of about 10 foot-candles or less, but is capable of transmitting at least a portion of the actinic rays of very bright light of brightness, of the order 10 or about 500 foot-candles or more.

In referring to the quality of the colored dye as substantially opaque" to the actinic rays of ordinary subdued daylight or the like and as capable of transmitting or transparent to" a 15 portion of the actinic rays of very bright light, it is of course understood that such opacity or transparency is a relative quality which can be reduced to an absolute quality only by taking into'account the element 01' time. Thus, even a go colored dye which, in the form of a film over a photo-sensitive emulsion, is "substantially opaque to the actinic rays-of a subdued light within the'meaning of the term as used herein, will pass a sufilcient-quanta of suchrays', if exposed g5 to the subdued light for a long enough period of time, to fog the paper; and conversely, even if the dye is capable of transmitting" a portion of the actinic rays of very bright light within the meaning of that term as herein employed, it is possible to expose the paper to such a light for so short a period of time that no perceptible effect of the exposure is to be observed. These terms are therefore employed herein in a relative sense and are to be interpreted in the light of common practice in photographic printing operations. For example, in making a contact photographic print it is awkward to have to expose the paper to a bright light of the order of 500 footcandles, in brightness for aperiod of time much 0 greater than about one minute. If much more time than this is required for a colored dye applied over the surface of a sensitive emulsion to pass sufiicient actinic rays of such bright lightproperly to expose the emulsion, the dye film ordinarily (except in cases where extremely slow" paper is desired) is regarded, for the purposes of the invention, as not capable of transmitting a sufil'cient portion of the actinic rays of the bright light. On the other hand, for example, the ordinary amateur printing operation requires a totaltime (from start of preparation for exposure to fixed print) of about five minutes or less, and if paper having its. sensitive emulsion coated with a colored dye fogs appreciably upon 55,

exposure for such a period of time (or even' for ten or fifteen minutes) to subdued light of a brightness of about 10 foot-candles or less, it is ordinarily regarded as not substantially opaque to the actinic rays of such light. But if the dye is of such character as to protect thesensitive emulsion from fogging upon exposureof the paper to ordinary subdued indoor light for the length of time required to complete the printing operation, and if the dye does permit passage of actinic rays to a sufiicient extent to enable proper exposure of the paper by a. bright light in a period of time reasonable for the nature of the particular printing operation, the dye is regarded as.

having the'aforementioned qualities of opacity to actinic rays of subdued white light and transparency to actinic rays of bright light, as these terms are used herein and in the appended claims.

For common black and white printing in halftones, the dye further is of such character that, upon immersion of the paper in a solution for development or fixing of a photographic image (or upon suitable washing after development and fixing), the color imparted thereby to the surface of the paper is discharged. Preferably the, color of thedye is discharged upon immersion of the paperin the fixing solution, for it is desirable to continue the protection provided by thedye during immersion of the paper in the developing solucator dyes will be discharged. It is-not necessarslightly acid) and will remain colored thereon for normal periods of storage and during immersion of the paper in the ordinary slightly alkaline developing solution. Upon subsequent imersion of the paper in the conventional slightly acid fixing and hardening solution, the color of such indiily characteristic of suitable indicator dyes, however, that their color is discharged by the acidity of the fixing solution. Rosolic acid, which isan especially satisfactory dye of the indicator class, appears to have its color discharged by a bleaching action of the acid sulphite fixing solution, and the color of nitrophenols, which also are dyes of the indicator class, are best discharged by immersion of the paper before or after fixing, in ethyl alcohol.

A number of indicators have been employed as dyes in accordance with the invention with varying degrees of success. Phenolphthalein, which in alkaline solution is pink, has been employed in the colored condition as a thin film over the photo-sensitive emulsion of a printing paper. Phenolphthalein retains its color in the usual alkaline developing solution, but upon immersion of the paper treated therewith in a standard slightly acid fixing solution the color is substantially completely discharged. Phenolphthalein, however, does not provide very satisfactory protection for the sensitive emulsion even in subdued light, and its use therefore is not recommended. Its pinkish color was not sufiiciently deep toexclude the damaging actinic rays of ordinary subdued white light, and, moreover, it tended to turn colorless upon standing in contact with the sensitive emulsion. This latter disadvantage could be overcome onlyby considerably increasing the valkalinityof the emulsion, but this expedient so increased the speed of the emulsion that the protective character of the phenolphthalein was more than offset. For this reason it is generally undesirable to employ an indicator dye that requires an alkaline environment to maintain it in the colored state.

Ortho, meta and para nitrophenols have also been employed, and being, in neutral and mildly alkaline solutions, deep yellow to orange in color,

provide good protection for the photo-sensitive emulsion. Some difficulty is apt to be experienced, however, in securing complete discharge of the color of these compounds by means of the sulphite fixing solution usually is necessary to secure complete discharge of the color, and after the fixing solution has been used a number of times it acquires ayellowish color itself and to a considerable extent loses its power to discharge the color of the dye. But by dipping the paper in ethyl alcohol before or after completion of the fixing and hardening operation, the color of these dyes can be discharged quite speedily.

Picryl methyl'nitramine, which is yellow to brown in alkaline solutions and colorless in acid, is a moderately satisfactory indicator for use in accordance with the invention, but some difficulty is experienced in applying a coating of sufiicient depth of, color adequately to protect the film and its color is somewhat difiicult to discharge.

One of the most satisfactory indicators for use in accordance with the invention, is rosolic acid, which is of orange color in relatively low concentration in substantially neutral solutions, but turns colorless upon immersion in the usual slightly acid sulphiteor metabisulphite fixing solution, and in general the use of this compound is preferred. Its natural orange color (which is apparent with the compound in low concentration in substantially neutral solutions) provides ex cellent protection for photo-sensitive emulsions, and the fact that its color does not depend upon the maintenance of a markedly alkaline environment makes use of this compound particularly advantageous. In fact, its natural orange color provides better protection for the emulsion than does the reddish color it exhibits in alkaline solutions. Moreover, the speed with which its color is discharged upon immersion in a sulphite fixing solution renders it particularly easy to employ.

The rosolic acid or other indicator or dye is applied to ordinary photographic printing paper as a separate coloredfilm over the exposed surface of the photo-sensitive, emulsion (which may be any suitable emulsion such as the common silver chloride emulsion), preferably after the latter' amount of indicator or dye thus applied is sufflcient to form a film deep enough in color to be substantially opaque (as hereinbefore defined) to the actinic rays of light of brightness oi the order of about 10 foot-candles, but transparent (as hereinbefore defined) to at least a portion of the actinic rays of a very bright light of the order of photographicprinting paper, coated for example, with the usual silver chloride emulsion, sat-. isfactory protection has been obtained with dyes forming a film colored a, moderately deepyellow, orange, tan or light brown, or a deep red. Blue or violet colored dyes are not recommended for such paper.

In employing rosolic acid; for example, a solu tion of this compound in an alcoholic solvent is appliedover the emulsion surface of a standard photographic paper by any suitable coating operation, as by spraying, dipping or painting, pref erably after the emulsion has become substantially completely dried. The solution employed should contain at least about 2% rosolic acid in,

order sufiiciently to color the surface of the paper, and in. general it is preferred to employ a solution containing about 2 to,3% rosolic acid. Such a solution colors the surface of the paper a moderately deep orange, which substantially excludes theactinic rays of ordinary indoor light from the photosensitive emulsion.

\ It is important that the solution of rosolic acid or other indicator or dye be applied uniformly and without theroccurrence of flutter or unevenness of coating on the paper, for otherwise theopacity of the dye film to actinic'rays will vary from point to point on the paper and it will not be possible to expose the paper uniformly. In the case of rosolic acid, if it is simply dissolved in ethyl alcohol and the alcohol solution is spread on the emulsion for example, the solvent evaporates so rapidly that nonuniformcoating or flutter is apt to result. For. this reason, it is preferred to apply the rosolic acid in solution in an ethyl alcohol-water solvent containing about 20% by weight of water. It is'preferableto use distilled water in the alcohol-water solvent, for tap water commonly is alkaline enough to convert the color. ofthe rosolic acid from its natural orange to the less desirable red; While it is possible to use a solvent containing considerably more than 20% and up to 61% water '(aboveithis latter concentration of ..water the rosolie acid tends to precipitate), the use of such high water" concentration in the solvent leads to dimculties in securing substantially complete color-dis charge in the fixing bath. Itis also advantageous ordinarily to incorporate in the solution a non-i. hygroscopic material capableof retarding the rate of evaporation of the solution, such as a small percentage of the order of 1% by weight of the solvent of a sugar or sugar-like compound.

Very satisfactory results have been obtained using rosoiic acid dissolved in a solvent employing ethyl alcohol and water in equal parts by weight and containing about 0.75% by weight of a product available under the trade name Yumidol Special, which is a colorless refined, water solution containing about sorbitol (a sugarlike, hexahydric alcohol), and which is a viscous, non-hygroscopic, colorless liquid, soluble to the extent necessary both in alcohol and water. Fructose and other similar materials may also be employed, but the use of glycerine, ethylene glycoland the like is excluded because these materials are so hygroscopic that they are apt to render the emulsion tacky and cause thereto if applied thereover.

Paper prepared in accordance with the invention is employed by first exposing it in a contact printing frame to a very bright light of brightness of the order of 500 foot-candles. For this purpose, useof the photographic printing method and apparatus defined in my copending application Serial'No. 23294 5, filed September 28, 1938,

-is especially satisfactory. Although it is, possible under special conditions to print onthe paper of the invention at a distance, an extremely intense lightor a well-focused one is required, and this practice is not recommended to the 'amateur. Even in making contact prints it is important that the paper be held close 'to the source of light and that the distribution of light over itssurface be uniform in order thatit may be properly exposed. s

After exposure, the paper .is immersed in a developing solution for purposes of development of the photographic image formed by the exoping solutions suitable for-the type of emulsion used on the paper may be employed. One such developing solution that has been employed with success is a compound consisting of about 3.1

grams Elon (a well-known developing reagent manufactured by the Eastman Kodak Co.) about 45 grams hydroquinone, about 67.5 grams sodium phenolphthalein, in the developer for the purpose of excluding actinic rays therefrom. Rosolic acid turns to a red-color in the standard alkaline developing solutions, and when this color it'does not provide as complete protection against foggin'g' as it. does when orange in color.

' After immersion of the paper in the developer for a suitable period of time, it is transferred to a fixing bath in which thedeveloped photographic image is fixed and in which, preferably,

the color of the dye is discharged. Any standard fixing bath maybe employed, such as the well-knownwater solution of about 480 grams sodium thiosulphate (hypo), about 30 grams sodium sulphite or sodium metabisulphite, about 30 'grams alum, and about 96 cc. of- 28% acetic acid dissolved in about 2160 cc. of water. In the [preferred application of the invention employing rosolic acid as the dye, the color of the rosolic acid 'is quickly discharged in such a fixing bath -.j and-a clear black and white print is obtained. .-,Al1;of these printing operations may be carried out in a subdued light of the order of about" 10 foot-'candles in brightness. I

Rosolic acid generally is noted as turning from red in alkaline solution to yellow or yellow brown in acid, I but in the fixing solution its color 'is substantially completely discharged. It therefore appears that a bleaching action of the sulphite dissolved in the fixing bath is, at least in part, responsible fof the color change. The acid of the bath seems toplay some part in this change, however, for in the alkaline developing bath, which also usually contains some sodium sulphite, the. color is changed only to a red, and is not completely discharged} v In the-foregoing specification and in the claims particular reference is made to photographic printing paper having a paper backing. Most photographic paper does in fact have a backing of paper, but in some cases a backing of some other flexible material is employed. It is understood that the process of the invention is fully applicable to products backed with such other flexible material (as Celluloid or cellulose acetate filmyas it may be desired; to employ. If

. l5 posure. Any of the standard well-known develthe backing is transparent, the dye used is applied in a manner to protect the emulsion from light on both sides thereof, as by applying. it to the back of the backing as well as over the exposed surface of the emulsion. Otherwise no substantial departure need be made from the procedure set forth above.

a I claim:

1. A photographic printing paper adapted to be printed upon, developed and fixed in white light, comprising a paper backing, a coating of a photo-sensitive emulsion applied to a surface of said backing, and rosolic acid in its colored state applied as a separate film over the exposed paper at least for a short period of time to subdued white light with fogging, butbeing sufilciently transparent to the actinic rays of very bright light to enable formation on the lightsensitive emulsion of a photographic image by exposure of the dye-coated surface of the paper to a brightlight.

2. A photographic printing paper adapted to be printed upon in half-tones, developed and fixed in white light, comprising a substantially opaque paper backing, a coating of a photo-sensitive emulsion applied to a surface of said backing, and rosolic acid in its colored state applied as a separate film over the exposed surface of said emulsion, said rosolic acid film being sufficiently deep in color to be substantially opaque to the actinic rays of subdued daylight or artificial white light of brightness of the order of about 10 foot-candles, but being capable of transmitting at least a sufficient amount of the actinic rays of very bright light of brightness of the order of 500 foot-candles to enable formation on the emulsion of a photographic image, whereby the emulsion-coated surface of said paper may be exposed at least for a short period of time to subdued white light without fogging, but may be printed upon by exposure of its dyecoatd surface to a bright light.

3. In printing photographically on a photographic paper comprising a photo-sensitive emulsion on a suitable backing, the improvement which comprises enabling printing in half-tones, developing and fixing in ordinary subdued daylight or artificial white light of a photographic image on said paper by applying to the exposed surface of the photo-sensitive emulsion-a separate film of rosolic acid in its colored state, said rosolic acid film being applied to such a depth of color as to be substantially opaque to the actinic rays of subdued light of brightness of the order of about 10 foot-candles but capable of transmitting at least a sufilient amount'of the actinic rays of very bright light of brightness of the order of 500 foot-candles to enable formation on the emulsion of a photographic image, exposing the rosolic acid coated surface. of said paper in contact witha suitable negative to a very bright light, immersing the exposed paper in a suitable developing solution to develop the photographic image thereon, and subsequently 1mmersing the paper in an acidic sulphite fixing solution in a manner such that the developed pho- 'the photo-sensitive emulsion a separate film, of

rosolic acid in its colored state, said rosolic acid film being applied to such a depth of color as to be substantially opaque to the actinic rays of subdued light of brightness of the order of about 10 foot-candles but capable of transmitting at least a suflicient amount of the actinic rays of very bright light of brightness of the order. of 500 foot-candles to enable formation on the emulsion of a photographic image, exposing the rosolic acid coated surface of said paper in contact with a suitable negative to a very bright light, thereafter immersing'said paper in a developing solution containing a dye of such color and in such concentration that actinic rays of ordinary daylight or artificial white light are substantially excluded from said solution, and subsequently immersing said paper in an acidic sulphite fixing solution in a manner such that the developed photographic image thereon is fixed and the color of the rosolicv acid is substantially completely discharged.

5. In the preparation of a photographic printing paper comprising a backing, a photo-sensi-. tive emulsion applied to a surface of said backing, and rosolic acid applied in a colored state as a separate'film' over the exposed surface of said emulsion, the method of forming said rosolic acid film evenly and uniformly on said emulsion which comprises dissolving rosolic acid in a solvent comprising about 80% ethyl alcohol and about 20% water by weight, and suitably coat-' ing the resulting solution .over the exposed emulsion surface of the emulsion-coated paper after the emulsion has become substantially completel dried. 6. In the preparation of a photographic printing paper comprising a backing, a photo-sensitive emulsion applied to a surface of said backing, and rosolic acid applied in its colored condition as a separate film over the exposed surface of said emulsion, the method of forming said rosolic acid film evenly and uniformly on said emulsion which comprises dissolving the rosolic acid in a solvent comprising about 20% by weight of water and about 80% by weight of ethyl alcohol and 'a small percentage of the order of 1% of a non-hygroscopic sugar, and suitably coating the resulting solution on the emulsion surface of the emulsion-coated paper after the emulsion has become substantially completely dried.

MAYSON H. TUCKER.