US3128180A - Hardened high-contrast photographic silver chloride emulsions and method of processing - Google Patents

Description

United States Patent HARDENED HIGH=ONTRAST PHOTOGRAPHIC SILVER CHLORIDE EMULSIONS AND METHOD OF PROCESSHNG Richard W. Helm and Charles A. Gofie, Rochester, N.Y., assignors to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey No Drawing. Filed July 2, 1958, Ser. No. 746,079

2 Claims. (Cl. 9627) This invention relates to photography, and more particularly, to high-contrast silver chloride emulsions and a method of processing the same.

In the graphic arts field, where it is desired to make photographic reproductions of line and half-tone material, it is customary to employ emulsions having extreme contrast. For this purpose, photographic silver chlorobromide emulsions are generally employed, the silver chloride content of the emulsions being at least about 60 mole percent. After exposure of the emulsions in the conventional way, either to a half-tone negative, or to an original through a vacuum contact screen, the emulsions are developed in a photographic developer having very low freesulfite content. Development is believed to proceed catalytically, and such development is commonly referred to in the graphic arts field as infectious development. In order to control the amount of free-sulfite in the developer, it is customary to employ sodium formaldehydebisulfite in the developer. This material then releases small amounts of sulfite to at least partially stabilize the developing solutions for short periods of time.

However, it has been found that developers containing sodium formaldehydebisulfite give results which are often erratic, depending upon the time of standing before use, exposure to air, etc.

Previously, it has been generally thought that the abovementioned catalytic development can only be obtained if the concentration of the sulfite ion is quite low. See J. A.C., Yule, Journal of the Franklin Institute, vol. 239, 1945, pages 221-230. It has been thought that the function of the sodium formaldehydebisulfite is to provide only very small amounts of the sulfite ion and prevent a loss of the high-contrast effect.

We have now found that certain photographic gelatinosilver-chloride emulsions containing at least 70 mole percent of silver chloride and controlled amounts of free formaldehyde can be processed to provide acceptable halftone reproductions even though processing is carried out in developers having large amounts of the sulfite ion present. Thus, it is possible to use photographic developers containing large amounts of sulfite without meeting storage difiiculties which accompany the use of photographic developers containing only small amounts of sulfite. The photographic developer generally employed in our developing compositions is a hydroquinone compound.

It is, therefore, an object of our invention to provide high-contrast photographic-gelatino-silver-chloride emulsions containing at least 70 mole percent of silver chloride and a predetermined amount of uncombined formaldehyde. Another object is to provide photographic elements containing the above-described silver chloride emulsions, wherein the dried coatings contain a predetermined amount of uncombined formaldehyde. Still another object is to provide a method of processing said silver chloride emulsions to provide high-contrast images using photographic developers which can contain large amounts of the sulfite ion. Another object is to provide developers for graphic arts use which need not contain sodium formaldehydebisulfite. Other objects will become apparent from a consideration of the following description and examples.

3,128,180 Patented Apr. 7, 1964 We have found that the addition of sufficient formaldehyde to the above-described silver chloride emulsions, so that the dried coatings contain at least 6 mg./ft. uncombined formaldehyde, provides a means of obtaining acceptable graphic arts images, even though the emulsions are processed in a photographic developer containing large amounts of antioxidant, such as sodium sulfite.

The silver chloride emulsions employed in our invention can contain from 70 to 100 mole percent of silver chloride. We have found that emulsions containing from 8 to 30 mole percent of silver bromide and from 70 to 92 percent of silver chloride are quite useful in our invention. We have further found that the silver halide emulsions can contain a small amount of silver iodide, such as 1 to 2 mole percent. Of course, it is to be understood that the silver halide emulsions always contain at least about 70 mole percent of silver chloride.

The amount of formaldehyde added to the silver chloride emulsions can vary, depending upon the degree of finishing, time of drying, etc. Since our invention uses gelatin emulsions, it is apparent that a portion of the formaldehyde will react with the gelatin to produce a degree of hardening, depending upon the amount of formaldehyde reacted or lost on drying. The amount of formaldehyde added to the wet emulsions can vary from about 0.1 to 2.0 moles per mole of silver present. The amount of uncombined formaldehyde remaining in the emulsions after drying will thus be at least 6 mg./ft.

The developers employed in our invention contain a hydroquinone compound as the active developer or developing agent. Such compounds include hydroquinone, isopropylhydroquinone, methylhydroquinone, 2,5-dimethylhydroquinone, etc.' The developer generally can contain from about 12 to 20 g./ liter of the hydroquinone developing compound. The developer will also contain an antioxidant, such as sodium sulfite, S-hydroxyquinoline, ascorbic acid, phloroglucinol, S-hydroxyethylhydrazine,

aminophenols (e.g., N-methyl-p-aminophenol, etc.), metasubstituted polyphenols, pyrazolidones (e.g., 3-phenylpyrazolidone, etc.), etc. Sodium sulfite is a particularly useful antioxidant, and we have found that from about 0.02 to 0.2 mole of sodium sulfite is suificient to stabilize the developer in the absence of other antioxidants. If desired, a mixture of the afore-mentioned antioxidants can be employed. Suflicient alkaline material should be employed to produce a pH of at least 9.0, and we have found that from about 70 to g./liter of sodium carbonate monohydrate and 10 to 50 g./liter of sodium bicarbonate are quite adequate. Other inorganic alkaline materials, such as sodium hydroxide, sodium acetate, etc., can be employed, if desired. The developer should also contain a small amount of a restrainer, such as potassium bromide, sodium bromide, etc. Generally, about 3 to 5 g./liter of restrainer are quite adequate. If desired, the developer can also contain other addenda, such as sequestering agents, e.g., tetrasodium pyrophosphate, etc. The developer can also contain sodium formaldehydebisulfite, if desired. Generally, from about 50 to 70 g./ liter of sodium formaldehydebisulfite is quite adequate. If it is desired to make a developer suitable for dry packaging, generally no sodium formaldehydebisulfite should be employed unless the developer is packaged as two separate units, with the sodiurn formaldehydebisulfite in one package and the alkaline material in a separate package.

The silver chloride emulsions of our invention provide a gamma, in some instances, as high as 11 to 14. The contrast gradient is sometimes as high as 9.0 to 9.2. The contrast gradient is a figure obtained from the characteristic curve of the emulsion by drawing a line from a point on the curve 0.10 density above gross fog to a point on the curve 0.4 log E units to the right of the first point. Thus, the contrast gradient is a gradient over a 0.4 log E exposure range, and includes a part of the toe of the curve.

The effectiveness of the new photographic elements of our invention and their use in combination with the abovedescribed developers can be measured by exposing the emulsions to a halftone image. After developing the exposed element, the pattern consists of areas commonly referred to as shadow dots and areas known as highlight areas. Intermediate between these two extremes are areas of varying size. The common method in the art for measuring the quality of the reproduction is to examine the shadow dot areas and the area referred to as 50% dots (i.e., /2 clear and /2 developed density). The quality of the shadow dots can be expressed on any convenient scale, but for the purposes of our invention, we prefer to grade on a scale where a is excellent and g is extremely poor, with varying degrees of quality proportionately graded between these two points. The quality of the 50% dots can conveniently be expressed in a progressive scale where 9 is excellent and 1 is extremely poor. A reproduction graded 6c is considered acceptable in dot quality. A shadow dot quality below c is generally not acceptable and a 50% dot quality below 6 is generally not acceptable.

The following examples will serve to illustrate further the advantages obtained accor ing to our invention. In these examples, the uncombined-formaldehyde content is expressed as 1X, 4X, 8X or 16X. 1X is considered a normal or customary amount and is approximately 2 mg./ft. while 4X is 6 mg./ft. 8X is 8 rng./ft. and 16X is 112 mg./ft. The developers used in the following examples had the following composition:

TABLE I Developer Compositions [Grams per liter] A B C D E F Hydroquinone 15.0 15.0 15.0 15.0 15.0 15.0 Sodium formaldehydebisulfite 50. 50. 0 50. 0 Sodium sulfite 1. 25 2. 7.0 10.0 Sodium carbonate. 35.0 35.0 35.0 35.0 35.0 35. 0 Sodium bicarbonate 22. 5 22. 5 22. 5 27. 5 22. 5 22. 5 Potassium br0mide 0.75 0.75 0.75 0.75 0.75 0.75 Sodium bisulfite 3.0 2.0 B-Hydroxyethylhydrazine Water to make 1 liter 2.0

EXAMPLE 1 A fine-grain photographic-gelatino-silver-chlorobromide emulsion, containing 80 mol percent of silver as the chloride and 20 mole percent as the bromide, was prepared according to the method described in MacWilliam U.S. Patent 2,756,148, issued July 24, 1956. To separate batches of the emulsion was added formaldehyde to give an uncombined formaldehyde content as outlined in Table II. The emulsions containing the uncornbined formaldehyde were then coated on a conventional film support, such as cellulose acetate or polystyrene, and the coatings dried in the usual manner. The dried coatings were then exposed, using tungsten illumination, to a step wedge through a magenta contact screen of the type described in How to Use the Kodak Magenta Contact Screen, Kodak Pamphlet No. Q21, 1956. The exposed coatings were then developed in the developer composition identified in the table and fixed in a conventional thiosulfate fixing bath.

The contrast gradient, as defined above, dot quality and degree of swelling of the coatings were then measured. The results are given in the following table. Also given in the table is the tray life for each of the developer compositions.

4 TABLE 11 Efiect of Hardener Content EXAMPLE 2 A fine-grain photographic-gelatino-silver-chlorobromide emulsion was prepared as described in US. Patent 2,756,148, the emulsion containing mole percent of the silver as chloride and 20 mole percent as the bromide. The emulsion was then treated with suflicient formaldehyde so that the dried photographic element contained 8 mg./ft. of uncombined formaldehyde. The emulsion was then coated on a conventional film support and dried. The dried coatings were then exposed through a magenta contact screen to a step wedge as in Example 1 above. In order to measure the relative speed of the coatings, only one-half of the surface was covered by the contact screen. Separate strips of the coating were then developed in Developer A of Table I to which the addendum had been added, as identified in the following table. The strips were developed for the times shown in the table, both with fresh developer and developer which had been aerated for six hours in an 8 x 10-inch tray containing 500 cc. of developer at 68 F. The strips were then fixed in a thiosulfate fixing solution. Contrast and dot quality of the area under the contact screen were measured and the speed of the emulsion was determined from the area of the coating not in contact wtih the magenta contact containing mole percent of the silver as chloride, and 10 mole percent as the bromide, was prepared according to the method of Us. Patent 2,756,148. The emulsion was then sensitized with a sulfur sensitizer, as disclosed in Sheppard U.S. Patent 1,574,944, issued March 2, 1925, and with a gold salt, as described in Damschroder U.S. Patent 2,597,856, issued May 27, 1952, or Yutzy et al. US. Patent 2,597,915, issued May 27, 1952. The emulsion was then divided into two separate batches. One batch was treated with suflioient formaldehyde to produce a normal content of uncombined formaldehyde (IX), while the other batch was treated with sufiicient formaldehyde to produce 16X unconrbined formmdehyde. Each of the batches was coated on separate film supports, as described above, and dried. The dried coatings were then exposed to a step wedge through a magenta contact screen, as described above, and developed in Developer D of Table I to which sodium sulfite had been added in the amounts shown in the table. After fixing in the usual manner, the contrast gradient and dot quality (shadow) Hafdener and Sulfite Variations 16X Hardener in Emulsion 1X Hardener in Emulsion Sodium Sulflte (to Developer D) (Grams per Liter) Dot Quality Dot Contrast Quality Contrast EXAMPLE 4 Separate batches of gelatino-silver-halide emulsions having the compositions shown in the following table were prepared and the emulsions then sensitized with a sulfur compound, as described in U.S. Patent 1,574,944. The emulsions were then coated on separate film supports and dried. The dried coatings were exposed to a step wedge through a magenta contact screen, which covered only half of the coating so that the emulsion speed could be determined. The coatings were developed for the shown in the following table, using the developers identified in the table. A separate series of strips were then processed in an identical manner, except that the developers were aerated for 6 hours, as described in Ex ample 2 above. Each set of strips was fixed and dried. The contrast and dot quality for each of the coatings are shown, as well as the development latitude to obtain optimum dot quality. The emulsion speeds shown in the table are relative. The results obtained were as follows:

TABLE V Conventional vs. Improved Systems the hydroquinone developer and sodium formaldehydebisulfite are in one package, while the alkaline ingredients are present in a separate package. Thus, Developers A, B and C, for example, should be mixed immediately prior to use. Even small quantities of antioxidants have been shown to provide useful results in extending the life of the developers, as can be see-n by reference to the above tables. As indicated above, the pH of the developer should generally be at least about 9.0, although we have found that particularly good results are obtained in those cases where the pH is at least about 9.6.

As indicated above, the photographic elements prepared acoording to our invention should contain at least about 6 mg/ft. of uncombined formaldehyde. in the coatings described in Examples 1-4 above, the photographic emulsions contained about 615 mg. of gelatin, 540 mg. of silver and 11.5 mg. of saponin (coating aid) per square foot. The amount of formaldehyde added to these coatings, to obtain the degree of hardness indicated in the examples, is indicated in the following tabulation, which compares the uncombined formaldehyde in the fresh coating before drying with the uncombined formaldehyde after drying.

The photographic silver chloride emulsions prepared according to our invention are useful in preparing halftone negatives from continuous tone originals without using a half-tone screen. For instance, if no sodium Emulsion Composition D Efiect of Aeration ev. Devel- Time Con- Emul. Dot Lat.

Ohlo- Bro- Hardoper (Min) trast Speed Quality (Min) Emul- Conride mide Iodide ener siou trast Speed 70 30 0 1X A 2% 6. 2 100 7c 1%; 28 2. 5

90 9 1 16X F 2% 7. 3 590 7b 24% 690 8. 6

The above table shows that the hardened chlorobromide hyde.

The silver chloride emulsions used in our invention can conveniently be ortho-sensitized or pan-sensitized with spectral sensitizing dyes. For instance, these emulsions can be spectrally sensitized by treating with a solution of a sensitizing dye in an organic solvent. sensitizing dyes useful in sensitizing the emulsions of our invention are described in BIDlOkGI et a1. U.S. Patent 2,526,632, issued October 24, 1950, Sprague U.S. Patent 2,503,776, issued April 11, 1950, and others.

The developers described in Table I above vary in their stability, as shown in the above examples. Developer E was found to provide good results during processing even after storage for 12 months in solution and showed only a 0.15 log E shift in speed, as compared with fresh developer. On the other hand, Developer A, stored under the same conditions, showed loss of activity in 24 hours and sulfite is employed in the developing compositions and the coatings are exposed to a continuous tone original, small, round spots appear in the reproduction which can be conveniently called pepper spots. These spots correspond roughly to a half-tone pattern. However, the results ob tained from the hardened emulsions of our invention are particularly outstanding when employed in combination with developers containing at least 0.01 mlolar sulfite ion, such as Developer B above.

The above coatings were dried for 4 to 6 minutes in a chamber having a dry bulb temperature of F. and a wet bulb temperature of 58 F.

The term uncombined formaldehyde as used herein means formaldehyde detectable by a chemical analysis, such as that of SB. Schryver, Proc. Royal Soc, B. vol. 82, page 226 (1910).

The term half-tone as used in the foregoing description and in the following claims means not only conventional dot patterns but also the well-known line patterns. That is, line screens can also be employed according to the above-described process to provide the unusual effects illustrated.

The photographic emulsions used in practicing our invention are, of course, of the developing-out type.

The emulsions can be chemically sensitized by any of the accepted procedures. The emulsions can be digested with naturally active gelatin, or sulfur compounds can be added such as those described in Sheppard U.S. Patent 1,574,944, issued March 2, 1926, and Sheppard et al. U.S. Patent 1,623,499, issued April 5, 1927, and Sheppard and Brigham U.S. Patent 2,410,689, issued November 5, 1946.

The emulsions can also be treated with salts of the noble metals such as ruthenium, rhodium, palladium, iridium, and platinum. Representative compounds are ammonium chloropalladate, potassium chloroplatinate, and sodium chloropalladite, which are used for sensitizing in amounts below that which produces any substantial fog inhibition, as described in Smith and Trivelli U.S. Patent 2,448,060, issued August 31, 1948, and as antifoggants in higher amounts, as described in Trivelli and Smith U.S. Patents 2,566,245, issued August 28, 1951, and 2,566,263, issued August 28, 1951.

The emulsions can also be chemically sensitized with gold salts as described in Waller et al. U.S. Patent 2,399,- 083, issued April 23, 1946, or stabilized with gold salts as described in Damschroder U.S. Patent 2,597,856, issued May 27, 1952, and Yutzy and Leermakers U.S. Patent 2,597,915, issued May 27, 1952. Suitable compounds are potassium choroaurite, potassium aurithiocyanate, potassium chloroaurate, auric trichloride and 2-aurosulfobenzothiazole methochloride.

The emulsions can also be chemically sensitized with reducing agents such as stannous salts (Carroll U.S. Patent 2,487,850, issued November 15, 1949), polyamines, such as diethylene triamine (Lowe and Jones U.S. Patent 2,518,698, issued August 15, 1950), polyamines, such as spermine (Lowe and Allen U.S. Patent 2,521,925, issued September 12, 1950), or bis(fi-aminoethyl) sulfide and its water-soluble salts (Lowe and Jones U.S. Patent 2,521,- 926, issued September 12, 1950).

The emulsions can also be optically sensitized with cyanine and merocyanine dyes, such as those described in Brooker U.S. Patents 1,846,301, issued February 23, 1932; 1,846,302, issued February 23, 1932; and 1,942,- 854, issued January 9, 1934; White U.S. Patent 1,990,507, issued February 12, 1935; Brooker and White U.S. Patents 2,112,140, issued March 22, 1938; 2,165,338, issued July 11, 1939; 2,493,747, issued January 10, 1950; and 2,739,- 964, issued March 27, 1956; Brooker and Keyes U.S. Patent 2,493,748, issued January 10, 1950; Sprague U.S. Patents 2,503,776, issued April 11, 1950, and 2,519,001, issued August 15, 1950; Heseltine and Brooker U.S. Patent 2,666,761, issued January 19, 1954; H'eseltine U.S. Patent 2,734,900, issued February 14, 1956; Van Lare U.S. Patent 2,739,149, issued March 20, 1956; and Kodak Limited British Patent 450,948, accepted July 15, 1936.

The emulsions can also be stabilized with the mercury compounds of Allen, Byers, and Murray U.S. Patent 2,728,- 663, issued December 27, 1955; Carroll and Murray U.S. Patent 2,728,664, issued December 27, 1955 and Leubner and Murray U.S. Patent 2,728,665, issued December 27, 1955 the triazoles of Heimbach and Kelly U.S. Patent 2,444,608, issued July 6, 1948; the azaindenes of Heimbach and Kelly U.S. Patents 2,444,605 and 2,444,606, issued July 6, 1948; Heimbach U.S. Patents 2,444,607, issued July 6, 1948 and 2,450,397, issued September 28, 1948; Heimbach and Clark U.S. Patent 2,444,609, issued July 6, 1948; Allen and Reynolds U.S. Patents 2,713,541, issued July 19, 1955, and 2,743,181, issued April 24, 1956; Carroll and Beach U.S. Patent 2,716,062, issued August 23, 1955 Allen and Beilfuss U.S. Patent 2,735,769, issued February 21, 1956; Reynolds and Sagal U.S. Patent 2,756,147, issued July 24, 1956; Allen and Sagura U.S. Patent 2,772,164, issued November 27, 1956, and those disclosed by Birr in Z. wiss. Phot., vol. 47, 1952, pages 2-28; the quaternary benzothiazolium compounds of Brooker and Stand U.S. Patent 2,131,038, issued Septemher 27, 1938; and the zinc and cadmium salts of Jones U.S. patent application Serial No. 493,047, filed March 8, 1955.

The emulsions may also contain speed-increasing compounds of the quaternary ammonium type of Carroll US. Patent 2,271,623, issued February 3, 1942; Carroll and Allen U.S. Patent 2,288,226, issued June 13, 1942; and Carroll and Spence U.S. Patent 2,334,864, issued November 23, 1943; and the polyethylene glycol type of Carroll and Beach U.S. Patent 2,708,162, issued May 10, 1955.

The emulsions may contain a suitable gelatin plasticizer such as glycerin; a dihydroxy alkane such as 1,5-pentane diol as described in Milton and Murray U.S. application Serial No. 588,951, filed June 4, 1956; an ester of an ethylene bis-glycolic acid' such as ethylene bis(met'nyl glycolate) as described in Milton U.S. application Serial No. 662,564, filed May 31, 1957; bis-(ethoxy diethylene glycol) succinate as described in Gray U.S. application Serial No. 604,333, filed August 16, 1956, or a polymeric hydrosol as results from the emulsion polymerization of a mixture of an amide of an acid of the acrylic acid series, an acrylic acid ester and a styrene-type compound as described in Tong U.S. patent application Serial No. 311,319, filed September 24, 1952. The plasticizer may be added to the emulsion before or after the addition of a sensitizing dye, if used.

The emulsions may contain a coating aid such as sapomin; a lauryl or oleoyl monoether of polyethylene glycol as described in Knox and Davis U.S. Patent 2,831,766, issued April 22, 1958; a salt of a sulfat'ed and alkylated polyethylene glycol ether as described in Knox and Davis U.S. Patent No. 2,719,087, issued September 27, 1955; an acylated alkyl taurine such as the sodium salt of N-oleoyl-N-methyl taurine as described in Knox, Twardokus and Davis U.S. Patent 2,739,891, issued March 27, 1956; the reaction product of a dianhydride of tetracarboxybutane with an alcohol or an aliphatic amine containing from 8 to 18 carbon atoms which is treated with a base, for example, the sodium salt of the monoester of tetracarboxybutane as described in Knox, Stenberg and Wilson U.S. patent application Serial No. 485,812, filed February 2, 1955; a water-soluble maleopimarate or a mixture of a water-soluble maleopimarate and a sub,- stituted glutamate salt as described in Knox and Fowler U.S. Patent 2,823,123, issued February 11, 1958; an alkali metal salt of a substituted amino acid such as disodium N-(carbo-p-tert. octylphenoxypentaethoxy)glutamate as described in Knox and Wilson U.S. patent application Serial No. 660,679, filed July 30, 1956; or a sulfosuccinamate such as tetrasodium N-(1,2-dicarboxyethyl)- N-octadecyl sulfosuccinamate or N-lauryl disodium sulfosuccinamate as described in Knox and Stenberg U.S. patent application Serial No. 691,125, filed October 21, 1957.

In the preparation of the silver halide dispersions employed for preparing silver halide emulsions, there may be employed as the dispersing agent for the silver halide in its preparation, gelatin or some other colloidal material such as colloidal albumin, a cellulose derivative, or a synthetic resin, for instance, a polyvinyl compound. Some colloids which may be used are polyvinyl alcohol or a hydrolyzed polyvinyl acetate as described in Lowe U.S. Patent 2,286,215, issued June 16, 1942; a far hydrolyzed cellulose ester such as cellulose acetate hydrolyzed to an acetyl content of 1926% as described in U.S. Patent 2,327,808 of Lowe and Clark, issued August 24, 1943; a water-soluble ethanolamine cellulose acetate as described in Yutzy U.S. Patent 2,322,085, issued June 15, 1943; 21 polyacrylamide having a combined acrylamide content of '3060% and a specific viscosity of 025-15 on an imidized polyacrylamide of like acrylamide content and viscosity as described in Lowe, Minsk and Kenyon U.S. Patent 2,541,474, issued February 13, 1951; zein as described in Lowe U.S. Patent 2,563,791, issued August 7, 1951; a vinyl alcohol polymer containing urethane carboxylic acid groups of the type described in Unruh and Smith US. Patent 2,768,154, issued October 23, 1956; or containing cyano-acetyl groups such as the vinyl alcohol-vinyl cyanoacetate copolymer as described in Unruh, Smith and Priest US. Patent 2,808,331, issued October 1, 1957; or a polymeric material which results from polymerizing a protein or a saturated acylated protein with a monomer having a vinyl group as described in US. application Serial No. 527,872 of Illingsworth, Dann and Gates, filed August 11, 1954.

If desired, compatible mixtures of two or more of these colloids may be employed for dispersing the silver halide in its preparation. Combinations of these antifoggants, sensitizers, hardeners, etc., may be used.

The invention has been described in detail with par= ticular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be efiected Within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

What we claim as our invention and desire secured by Letters Patent of the United States is:

1. In the preparation of a half-tone pattern by exposing a dried, thin photographic silver halide emulsion layer on a photographic support to a half-tone image and developing the resulting exposed silver halide emulsion layer with a photographic aqueous developer, the improvement which comprises employing a high-contrast photographic gelatino-silver halide emulsion layer containing at least 6 mg. per square foot of uncombined formaldehyde, the quantity of formaldehyde present in said silver halide emulsion layer prior to drying being between about 0.1 and 2.0 mole per mole of silver halide, said silver halide emulsion containing at least 70 mole percent silver chloride, and a photographic aqueous developer having a pH of at least 9.0 and containing a hydroquinone as the active developing agent and at least 0.01 molar of sulfite ion.

2. In the preparation of a half-tone pattern by exposing a dried, thin photographic silver halide emulsion layer on a photographic support to a half-tone image and developing the resulting exposed silver halide emulsion layer with a photographic aqueous developer, the improvement which comprises employing a high contrast photographic gelatino-silver halide emulsion layer containing at least 6 mg. per square foot of uncombined formaldehyde, the quantity of formaldehyde present in said silver halide emulsion layer prior to drying being between about 0.1 and 2.0 mole per mole of silver halide, said silver halide emulsion containing at least mole percent silver chloride, 8 to 30 mole percent silver bromide and 0 to 2 mole percent silver iodide, and a photographic aqueous developer having a pH of at least 9.6 and containing hydroquinone as the active developing agent, at least 0.01 molar of sodium sulfite, sodium formaldehyde-bisulfite and potassium bromide as a restrainer.

References Cited in the file of this patent UNITED STATES PATENTS 2,309,497 Albers et al. Jan. 26, 1943 2,533,650 Wattier Dec. 12, 1950 2,585,596 Stanton Feb. 12, 1952 2,586,168 Kaszuba Feb. 19, 1952 2,652,345 Jones Sept. 15, 1953 2,716,059 Yutzy et al. Aug. 23, 1955 2,725,295 Allen et al. Nov. 29, 1955 2,754,208 Conrad July 10, 1956 2,756,148 MacWilliam July 24, 1956 2,845,349 Schwarz July 29, 1958 2,887,377 Dickerson May 19, 1959 2,902,367 Welliver et al. Sept. 1, 1959 3,030,209 Henn et al. Apr. 17, 1962 OTHER REFERENCES Yule: Journal of the Franklin Institute, vol. 239, 1945, pages 221-230. (Copy in Sci. Library T1F8.)

Mees: The Theory of Photographic Process, 1942, Macmillan Co., NY. (Preface, pages vii-viii.) Copy in Sci. Library TR a14t.

Claims (1)

1. IN THE PREPARATION OF A HALF-TONE PATTERN BY EXPOSING A DRIED, THIN PHOTOGRAPHIC SILVER HALIDE EMULSION LAYER ON A PHOTOGRAPHIC SUPPORT TO A HALF-TONE IMAGE AND DEVELOPING THE RESULTING EXPOSED SILVER HALIDE EMULSION LAYER WITH A PHOTOGRAPHIC AQUEOUS DEVELOPER, THE IMPROVEMENT WHICH COMPRISES EMPLOYING A HIGH-CONTRAST PHOTOGRAPHIC GELATINO-SILVER HALIDE EMULSION LAYER CONTAINING AT LEAST 6 MG. PER SQUARE FOOT OF UNCOMBINED FORMALDEHYDE, THE QUANTITY OF FORMALDEHYDE PRESENT IN SAID SILVER HALIDE EMULSION LAYER PRIOR TO DRYING BEING BETWEEN ABOUT 0.1 AND 2.0 MOLE PER MOLE OF SILVER HALIDE, SAID SILVER HALIDE EMULSION CONTAINING AT LEAST 70 MOLE PERCENT SILVER CHLORIDE, AND A PHOTOGRAPHIC AQUEOUS DEVELOPER HAVING A PH OF AT LEAST 9.0 AND CONTAINING A HYDROQUINONE AS THE ACTIVE DEVELOPING AGENT AND AT LEAST 0.01 MOLAR OF SULFITE ION.