US2644756A

US2644756A - Photographic process for forming a positive transfer image

Info

Publication number: US2644756A
Application number: US727383A
Authority: US
Inventors: Edwin H Land
Original assignee: Polaroid Corp
Current assignee: Polaroid Corp
Priority date: 1947-02-08
Filing date: 1947-02-08
Publication date: 1953-07-07
Anticipated expiration: 1970-07-07

Description

July 7, 1953 E. H. LAND 2,644,756

PHOTOGRAPHIC PROCESS FOR FORMING A POSITIVE TRANSFER IMAGE Filed Feb. 8, 1947 I '2 Base Layer Phoisenslflve Layer l0 l6 j" l4 Image ccrrylng Layer Confaincr FIG. I

IN TOR Patented July 7, 1,953

PHOTOGRAPHIC PROCESS FOR FORBIING A POSITIVE TRANSFER IMAGE Edwin H. Land, Cambri Polaroid Corporation,

poration of, Delaware dge, Mass., asslgnor, to Cambridge, Mass., a cor- Application February 8, 1947, Serial No. 727,383

4 Claims. I

v Thisv application; relates to photography, .and to novel photographic processes in general.

This invention relates more particularly to processes of the type. where a positive image is formed-from a latent'negative image in a silver halide photosensitive layer by creating positive image-forming components under the selective control of the development of the latent image and by utilizing these image-forming components for creating the positive image. With such processes, staining of the highlights of the positive image is sometimes encountered due to the existence of unused developer in'stain-forming condition in'sai'd highlights. a g

It is a. principal object of the present invention photosensitive layer and the image-carrying layer, thedeveloper therein develops the exposed photosensitive material and the silver halide solto provide improved processes offithe above type .7

and improved products foruse with such processes whereby staining of the highlightsof the positive image is prevented. v

These and other objects of the invention will in part be obvious and will in part appear hereinafter. v The invention accordingly comprises the several'steps' and the relation and order of one or more of' such steps with respect to each of the others, which are exemplified in the following detailed disclosure; and the scope of the application of which willbe indicated inthe claims.-

For a fuller understaiiding'ofthe nature and objects of the invention, reference should be had u to the following detailed description, taken in connection 1 with rth x. accompanying drawing wherein: Figure 1 is an exaggerated cross-sectionalview of a preferred composite photographic film unit I embodying the present invention.

In the photographic processes with which this invention is particularly involved, a sheet of photosensitive material preferably a silver halide, is

. exposed-to actinic light to create therein a latent negative image. This latent image is developed and a positive image thereof is formed on an image-carrying layer, preferably by creating be tween the two layers a uniform film of a viscous alkaline developer solution containing a substance capable of forming positive image-forming I components. This latter substance, in a preferred form of the invention, comprises a silver halide solvent such as sodium thiosulfate. With such a film of liquid composition between the exposed ventforms soluble complex ions with the unex posed photosensitive material. These'complex ions are dissolved and are transported to the surface of the image-carrying layer where :they 'are converted, by the developer, to colloidal particles comprising silver, these particles constituting a positive image of the latent negative image. i The creation of this layer of liquid, including the developer, is a mechanical process and subject to considerable variation as the result of different conditions of temperature, etc., during the spreading of the liquid. Therefore, it is desirable, in most casesQto include in the'layer of liquid composition more developer-per unit area .than would ordinarily be requiredto'just developthe exposed photosensitive material so as to fully cover and develop the negative image; Much of the excess developer remains on the image-carrying layer containing the positive image. The principal feature of the present invention is the prevention of .any stain due to oxidation of -viding a strong antioxidant in the liquidecompfo;

sition or on one of the layers in' positionto'be dissolved by the liquid composition as it spreads between these layers. This antioxidant is preferably one. whose oxidation product is Iwh'i-teor colorless andalso one which has at least the ability to reduce the silver complexes to silver and preferably has'some ability for assisting in developing the latent negative image. w

In a preferred form of the invention the anti oxidant is included on the image-carrying layer and its eilectiveness is increased by use in combination with a substance of acid reaction. I Referringnow to Fig. l there is shown a preferred form of a film unit embodying the present invention. In Fig. 1 there is provided a photosensitive layer I 0, preferably carried by a suitable base layer l2, and an image-carrying layer l4. Between these two layers there is preferably positioned the container. "5 having therein a liquid composition. l

In a preferred modification of the invention the photosensitive layer I 0 comprises a silver halide photosensitive material coated upon a suitable cellulosic film base l2. The image-carrying layer comprises, in a preferred form, a sheet of baryta paper which has been treated by coating thereon a thin layer of a material prepared as set forth in the following nonlimiting example:

Example 1 The following ingredients are placed in a mechanical mixer and preferably added in the order named, While being continuously mixed: 192 cc.,of a. 40%,Water solution of neutral lead acetate,

30 gm. of silica aerogel (Santocel C Monsanto) 50 cc. of a /5% water solution of sodium sulfide cc. of a 2% water solution of'sodium'tsulfide 66 cc. of a 1% water solution cupric acetate 36 cc. of a 15% water solution of ascorbic acid.

When an extremely stablepicture isdesir'ed;

it is preferred, in some cases, to place the coating of Example 1 on a sheet of baryta,,paper which has been previously dipped as set forth in the following nonlimiting example: v 7 Escample, 2 I I Asheet'of barytapaperis run through a'%% neutral lead "acetate bath for 1. minute, dried,

run through a 4 sodium sulfide bathfor 2 seconds, dried, and then run through a, bath containing 1% neutral lead acetate, 10% cadmium acetate and zincxnitrate for 1 minute. 'Itzisalso possible to use, in place of the baths of Example 2, a single bath containingcadmium acetate, neutral lead acetate, and; zinc nitrate. A liquid composition the container l6 preferably comprises a developer such as hydroquinone, an' alkali such as sodium hydroxide-a silver halide solvent such as sodium thiosulfate,

a preservative such as sodium sulfite, and a filmforming material, which in a preferred form is sodium" carboxymethyl cellulose. sThere is also included a suflicient amount of water to carrytheabove-mentioned elements in "solution- A suitable liquid composition may comprise:

Sodium sulfite c 18 Sodium hydroxide 574.6 Sodium thiosulfate t 1%.5, Citric acid I 38,5 Hydroqui-none .52

-Various equivalentsmay be used in the'abovementioned liqu'id'composition and itis equally possible to substitute, for the film-forming so dium carboxyinethyl cellulose, other film form .theliquid-composition; v iia" the-latent negative image in the photosensitive layer" and the silver halide solvent forms with the unexposed "portions of the photosensitive layer soluble silver complexes. .-;The si lver halide complexes migrate to theimage' -carrying layer where they are converted into insoluble particles comprising silver 'by the=jointactionof the developer, the ascorbic *acid andfthe ,lead sulfide on the surface of the image-carrying layer. 7

"1 ;,Thegpositiveaimage on the image-carrying following nonlimit-in'gexamples layer is next separated from the photosensitive layrand there is foundtto exist a stable positive image on the surface of the image-carrying layer. The stability ofthe positive image ith respect to'heat, moisture; and-"radiation" is believed to *be 'due;'at 'least partially, 'to"the' aritioxidantl characteristics '-'of-" the -ascorbic acid whichprevents oxidation of any excess developer in the highlights of "the positive image. effect, in some .cases, is noticeably increased when the alkalinity of the positive image is lowered to a neutral oracid condition'by thei inclusion on the image-carrying layer'of a' substance-of .ac'id reaction such as'th'e metal salts "described in Example 2- Otherantioxidants may-beiused'onthe image carrying layer in place of', dr?in a'ddition to; the ascorbic acid iniEx'ampl'e' 11;! asset for h iii-the 1 Examples! 2 The mixture of Example lis modified by -replacing ,the ascorbic acidiwith lfl: cc. of axI5% water solution .sof; aminoguanidine'.-'

, wmp

The mixturelofExamplel is' modified wire placing-the. ascorbic acid -with;.12 cc. ,of a l5%- water solution oij-gaminourea. '1"; AnotherZ example of the, use, of ascorbic acid is set forth;below vvhen theplisted .ingredientsare mixed and applied; s inExample 1.

150. 0: 40% solutionvofneutral lead ing materials such as other alkali-inertwatersoluble polymers, for example hydroxyethyl cellulose', 'polymethacrylic acid, and aluminum car- 'boxymethyl cellulose. Equally, other developers, preservatives, "alkalies, and silver halide solvents may be used, and" other substances such as restrainers may be added where desired.

In the 'use of the embodiment of the invention shown in Fig. 1, thephotosensitive layer -H) is exposed to actinic light, either through the base layer l2, or by separating the photosensi- "tive layer 10 and the base layer [2 from the remainder of the film unit to allow direct exposure of the photosensitive layer 10 by light which does not pass through any" of theother acetate I Ellis-:01? .silicaaerogel 1.

60-:cc.pf a1.%' water solution-"ofso'dium sulfide 36 cc. of a 15%,,waterusolution Qf'5aSCOI'biC' acid A baryta image-' arrying layer is prepared for receiving the above mix byfdipping for about"30 seconds in a water s'olution- -containing by weight g 10% cadmium acetate, 1% "leadacetate an zine nitrate. o While it'is' preferred thatftlie antioxidant 'e included on the image -carryin'g a es-arse sociated' with the film'ju'ni't or some otherlayer inposition to befliss'olved by the liquid com position, this 'is not-essential; and satisfactory results have "been achieved byincluding the anti oxidant-, 'suf h as ascorbic acid, in the liquid corn' position.

In general it is desirable to include the antioxidant on the image-carrying layer since, during the most critical portion of the development of the negative image, 1. e., the initial development, the strongly alkaline solution of the developer is unaffected by the presence of the antioxidant which is being dissolved from the image-carrying layer; therefore its initial effect on the negative is not restrained by the antioxidant. This gives an undiminished capability for the developer in its initial stage of the process for the development of the negative image. As the development of the negative proceeds, the antioxidant is dissolved, thus somewhat restraining the capability of the developer. However, at this point the positive image is also forming which acts to localize the precipitation of silver from the silver complexes, there-by removing the necessity for extremely rapid and accurate development of the negative image. This antioxidant also assists in reducing the silver complexes to silver on the image-carrying layer; thus it acts as a developer for the positive image along with those portions of the developer which are unaffected by development of the negative image.

While a preferred form of the invention has been described, it should be pointed out that various modifications thereof are within the broad scope of the invention. For example, certain of the materials normally carried in the liquid composition may be included on the various layers of the film unit in position to be dissolved by the liquid as it is spread through the film unit. As an example of this, the sodium thiosulfate may be included on the image-carrying layer, and in some cases this modification of the invention is preferred.

Since certain changes may be made in the above process without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A photographic process for forming, by transfer, a positive print of a latent image contained in the silver halide emulsion of a photosensitive element wherein a single application of liquid to said element is effective to give a finished print of improved stability, which process comprises the steps of bringing a relatively uniform layerwise distribution of a processing liquid into contact with the photosensitive element so as to permeate said emulsion with said liquid, said layerwise distribution of processing liquid providing the entire mass of liquid for performing said processing; causing said liquid to permeate said photosensitive element while a print-receiving element is superposed therewith and providing, as reagents in said processing liquid, a silver halide developer characterized by its propensity for oxidizing in an alkaline environment to form stains, a silver halide solvent capable of forming transferable soluble silver complexes with the unexposed silver halide of said emulsion, an alkali and ascorbic acid, the oxidation characteristics of the latter being such that it serves as an antioxidant for said developer, said ascorbic acid being capable of cooperating with said developer in the reduction of the silver of soluble silver complexes; developing said emulsion layer with said processing liquid and transferring from said emulsion layer, by imbibition, at least part of said soluble silver complexes onto a print-receiving stratum supported by said print-receiving element; reducing by said processing liquid the silvcr ions of said soluble silver complexes to silver insaid print-receiving stratum to form an image in silver which is a positive of the subject matter of the latent image developed in the silver halide emulsion; and separating said stratum with said print-receiving element from said photosensitive layer, a quantity of said ascorbic acid being permanently retained in said stratum and inhibiting such residual amounts of said silver halide developer as may be in said stratum from forming stains therein.

2. The process of claim 1 wherein the developer is hydroquinone.

3. The process of claim 1 wherein the layerwise distribution of processing liquid is obtained by spreading the mass of processing liquid between the photosensitive element and the print-receiving element and wherein said reagents are contained in the processing liquid prior to its spreadmg.

4. The process of claim 1 wherein the ascorbic acid is initially carried in solid form upon one of said elements and is dissolved in the processing element during the confinement of said liquid between the outer surfaces of said elements.

EDWIN H. LAND.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 742,405 Eichengrun Oct. 27, 1903 1,574,944 Sheppard Mar. 2, 1926 1,821,281 Van Der Grinten Sept. 1, 1931 1,841,653 Van Der Grinten Jan. 19, 1932 1,928,192 Walker Sept. 26, 1933 1,956,230 Schmidt Apr. 24, 1934 2,315,966 Knott Apr. 6, 1943 2,352,014 Rott June 20, 1944 2,415,666 Weissberger Feb, 11, 1947 2,417,924 Gary Mar. 25, 1947 2,500,421 Land Mar. 14, 1950 2,543,181 Land n Feb. 27, 1951 FOREIGN PATENTS Number Country Date 879,995 France Dec. 10, 1942 OTHER REFERENCES published by The MacMillan 00., New

Claims

1. A PHOTOGRAPHIC PROCESS FOR FORMING, BY TRANSFER, A POSITIVE PRINT OF A LATENT IMAGE CONTAINED IN THE SILVER HALIDE EMULSION OF A PHOTOSENSITIVE ELEMENT WHEREIN A SINGLE APPLICATION OF LIQUID TO SAID ELEMENT IS EFFECTIVE TO GIVE A FINISHED PRINT OF IMPROVED STABILITY, WHICH PROCESS COMPRISES THE STEPS OF BRINGING A RELATIVELY UNIFORM LAYERWISE DISTRIBUTION OF A PROCESSING LIQUID INTO CONTACT WITH THE PHOTOSENSITIVE ELEMENT SO AS TO PERMEATE SAID EMULSION WITH SAID LIQUID, SAID LAYERWISE DISTRITBUTION OF PROCESSING LIQUID PROVIDING THE ENTIRE MASS OF LIQUID FOR PERFORMING SAID PROCESSING; CAUSING SAID LIQUID TO PERMEATE SAID PHOTOSENSITIVE ELEMENT WHILE A PRINT-RECEIVING ELEMENT IS SUPERPOSED THEREWITH AND PROVIDING, AS REAGENTS IN SAID PROCESSING LIQUID, A SILIVER HALIDE DEVELOPER CHARACTERIZED BY ITS PROPENSITY FOR OXIDIZING IN AN ALKALINE ENVIRONMENT TO FORM STAINS, A SILVER HALIDE SOLVENT CAPABLE OF FORMING TRANSFERABLE SOLUBLE SILVER COMPLEXES WITH THE UNEXPOSED SILVER HALIDE OF SAID EMULSION, AN ALKALI AND ASCORBIC ACID THE OXIDATION CHARACTERISTICS OF THE LATTER BEING SUCH THAT IT SERVES AS AN ANTIOXIDANT FOR SAID DEVELOPER, SAID ASCORBIC ACID BEING CAPABLE OF COOPERATING WITH SAID DEVELOPER IN THE REDUCTION OF THE SILVER OF SOLUBLE SILVER COMPLEXES; DEVELOPING SAID EMULSIONLAYER WITH SAID PROCESSING LIQUID AND TRANSFERRING FROM SAID EMULSION LAYER, BY IMBITION, AT LEAST PART OF SAID SOLUBLE SILVER COMPLEXES ONTO A PRINT-RECEIVING STRATUM SUPPORTED BY SAID PRINT-RECEIVING ELEMENT; REDUCING BY SAID PROCESSING LIQUID THE SILVER IONS OF SAID SOLUBLE SILVER COMPLEXES TO SILVER IN SAID PRINT-RECEIVING STRATUM TO FORM AN IMAGE INSILVER WHICH IS POSITIVE OF THE SUBJECT MATTER OF THE LATENT IMAGE DEVELOPED IN THE SILVER HALIDE EMULSION; AND SEPARATING SAID STRATUM WITH SAID PRINT-RECEIVING ELEMENT FROM SAID PHOTOSENSITIVE LAYER, A QUANTITY OF SAID ASCORBIC ACID BEING PERMANENTLY RETAINED IN SAID STRATUM AND INHIBITING SUCH RESIDUAL AMOUNTS OF SAID SILVER HALIDE DEVELOPER AS MAY BE IN SAID STRATUM FROM FORMING STAINS THEREIN.