US3471297A - Photomechanical emulsions containing a polyethylene glycol dicarboxylic acid ester - Google Patents

Description

United States Patent 3,471,297 PHOTOMECHANICAL EMULSIONS CONTAHNNG A POLYETHYLENE GLYCOL DICARBOXYL/I ACID ESTER Joseph A. Sprung, Binghamton, N.Y., assignor to GAF Corporation, New York, N.Y., a corporation of Delaware Continuation of application Ser. No. 253,331, Jan. 23, 1963. This application Dec. 22, 1966, Ser. No. 604,064 Int. Cl. G03c 1/28 U.S. Cl. 96-107 4 Claims ABSTRACT OF THE DISCLOSURE Photographic iilm having on a base a silver halide emulsion for half-tone reproduction with a gamma above 8, containing a polyethylene glycol ester of a dicarboxylic acid wherein the polyglycol moiety has a molecular weight from 4,000 to 9,000 and the ester has a molecular weight of at least 29,000, in a concentration of to 1,000 mg. per 100 g. of silver halide.

dium or low-contrast image, whereas emulsions used for u half-tone and line reproduction in the photomechanical and lithographie field must produce an extremely contrasting image so as to satisfy the critical standards of the lithographer and photoengraver.

The gradation of an emulsion and the iilm of which it is part is customarily defined by a graphic analysis of the response to light shown by the lilm under certain definite and accurately controlled conditions of exposure and development. For this purpose, the lm is exposed in a sensitometer and developed under controlled and standardized conditions. The resulting densities are measured and plotted on a graph against the exposure values which produce them. The line drawn through the resulting points is termed the characteristic curve or the H and D curve for that particular sample. Inasmuch as most photomechanical processes require a iilm of extremely high contrast, optimum results are obtained only when all of the highly exposed portions of the negative have the same high density and when the unexposed or underexposed portions of the film are completely clear. Thus, the characteristic curve of an ideal graphic arts lm would portray an abrupt exposure differential between the minimum and maximum density regions. The attainment of such ideal sensitometric characteristics are not presently possible, and the characteristic curves of iilms for half-tone and line copy purposes always possess a somewhat extended intermediate exposure range. As a result, the half-tone dot images will exhibit an undesirable fuzziness unless the exposure and development conditions are carefully controlled.

1 have now discovered that the quality of high-contrast emulsions used in the graphic arts iield can be improved 3,471,297 Patented Oct. 7, 1969 ICC by adding to the emulsions during their preparation and prior to their coating, a polyoxyalkylene glycol or polyoxyalkylene derivative containing at least 10 polyoxyalkylene groups in the molecule and having a molecular weight in excess of 440. I have further discovered that the photographic quality of developed high contrast emulsions can be improved by adding the above polyoxyalkylene compounds to lithographie developer solutions. Such developer solutions, as well as photo-sensitive emulsions, the lilms prepared therefrom, and the methods of developing such emulsions constitute the purposes and objects of this invention. Other objects Will be apparent from the following description.

The gelatin silver halide emulsions used in the preparation of graphic art films are unsensitized, orthochromatic or panchromatic, high-contrast emulsions. These emulsions are developed with the so-called infectious type developers which contain, in addition to a developing agent of the hydroquinone type, a mixture of paraformaldehyde and potassium metabisulte or the reaction product of a formaldehyde and sodium bisullite as described in U.S. Patent 2,313,523. The infectious developers normally produce images possessing gamma values of approximately 8.0. When development is carried out in the presence of polyoxyethylene derivatives (in the emulsion or developer) gamma values in the l5 to 18 range are readily obtainable.

The lithographic developers which are used in the infectious type of developers dilfer from the conventional developers by containing only a small and controlled amount of free sulte ions. The major amount of the alkali sulfte which is contained in the developer solution is kept in reserve in the form of a formaldehyde-bisulfite addition compound which acts as a sulte buier. If too much sulte is present, infectious development will not occur, and if too little is available, a high fog level will result.

The developers differ also from conventional developers to the extent that the development time is somewhat critical if images of maximum gamma are desired. Development times which are shorter or longer than the optimum durations will yield low gamma values. The highest gamma values are obtained within a development time ranging from 11/2 minutes to 41/2 minutes.

The silver halide used in the preparation of these emulsions is silver chloride, silver chlorobromide or silver bromide.

Small concentrations of iodide can be tolerated if the silver iodide content of the emulsion does not exceed 3.0 mole percent based on the amount of silver nitrate used in the preparation of the silver halide emulsions. When silver chlorobromide emulsions are used, the relative amount of halides generally ranges from 2 to 8 parts of chloride per part of bromide.

The amount of polyalkylene glycol or polyoxyalkylene derivative used ranges from l0 milligrams to 1000 milligrams per kilogram of liquid silver halide emulsion; the preferred range is between 50 and 500 milligrams per kilogram of silver halide emulsion. Expressed in terms of silver halide content, the amount of polyoxyalkylene compound used ranges from about 10 to 1000 milligrams per grams of silver halide. Expressed in terms of coated area, the amounts of polyoxyalkylene compound present in the finished and coated emulsion ranges from 1 to 100 milligrams per square meter, Whereas the amount of silver present in the linished coated emulsion ranges from 4 to 10 grams per square meter. When used in the concentration specied, the polyoxyalkylene compound produces a marked increase in contrast or a shortening of the intermediate exposure range of the sensitometric curve. As a result, the graphic art films produced from these emulsions, which are used in the half-tone and line processes, give much cleaner and darker dots which are sharp around the4 edges, whereas the dots prepared from conventional emulsions are dull and fuzzy thus leading to an inferior image.

When added to developer solutions, the polyoxyalkylene compounds are used in amounts ranging from 50 to 1000 milligrams per liter of developer solution.

In the preparation of the emulsions, polyoxyalkylene compounds are added during the ripening stage or just prior to coating in the form of an aqueous solution. The polyoxyalkylene compounds which I have found suitable for use with my invention have a molecular weight which ranges from 440 to about 5,000,000. These compounds include those which are prepared by condensing ethylene oxide with itself, such as the commercially available products Carbowax 4000 and Carbowax 6000, which are polyethylene glycols having molecular weights of 4,000 and 6,000, respectively. Polyethylene and polypropylene glycols having higher molecular weights are equally suitable.

Other polyoxyalkylene derivatives suitable for use with my invention include the mixed ethers formed by the condensation of long chain fatty alcohols with ethylene oxide such as polyoxyethylene lauryl ether, cetyl ether or oleyl ether. A typical example of these compounds is the reaction product of lauryl alcohol and ethylene oxide which contains about 35 oxyethylene units in the molecule. Compounds of this type are described in U.S. Patent 1,970,578. Other compounds described in this patent include the reaction products of ethylene oxide with carboxylic acids and amines, which I have also found highly satisfactory in carrying out my invention.

Condensation products of polyethylene glycol with the chlorides of dicarboxylic acids such as oxalyl chloride, succinyl chloride, adipyl chloride, sebacyl chloride, and phthalyl chloride are described in U.S. Patent 2,567,076. These compounds are prepared from polyoxyethylene glycols having average molecular weights between the range of 4,000 to 9,000. The resultant condensation products have molecular weights of at least 29,000 and constitute the preferred compounds of my invention.

It has been previously proposed to use these and similar polyoxyalkylene derivatives in commercial and portrait type emulsions which have a gamma or gradient on the order of 1 or 2. When the polyoxyalkylene derivatives are added to this type of emulsion, they increase the speed of these emulsions. However, when the high molecular weight polyoxyalkylene derivatives are added to the high contrast emulsions which are used with infectious type developers in the lithographie and photomechanical field for half-tone and line reproduction, they function in an entirely different way. The speeds of the emulsions are decreased in a rather drastic manner. However, this speed Vloss is compensated by other beneficial results including a very noticeable increase in contrast.

Most or all of the speed loss incurred by the use of these polyalkylene compounds can be regained by the gold sensitization of the emulsion during their preparation. The gold sensitization is now well known to persons skilled in the photographic art and reviewed inter alia by a F. W. H. Mueller in his paper Some Remarks on Gold Treatment of Photographic Silver Halide Emulsions published in the Journal of the Optical Society of America, vol. 39, pp. 494-496 (1949). Among the gold salts which may be used in this sensitization are the following: potassium aurate, potassium chloraurite, potassium bromoaurite, potassium iodoaurite, potassium auricyanide and potassium aurithiocyanate, or the corresponding sodium, calcium, strontium, cadmium or gallium salts. Complex organic gold salts may also be used, e.g. pyridino trichloro gold, ethylenediamine-bis-trichlorogold, diethyl-monobrom-gold and diethyl-gold-acetyl-acetone, and also the gold complexes with sulphur compounds such as thiourea.

The emulsions can also be treated with salts of the noble metals such as ruthenium, rhodium, palladium, iridium and platinum, all of which belong to Group VIII of the periodic table of elements have an atomic weight greater than 100. 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.

Some of the polyoxyalkylene compounds of my invention have a strong tendency to produce fog in theemulsion to which they are added. This fog increase can be counteracted by the use of certain antifoggants such as a water soluble benzene sullinic acid salt either alone or in combination with heterocyclic mono or polysuldes, with thiosulfonic acid derivatives, with cystine, with polysuldes or with polythionates, as described in U.S. Patents 2,385,762, 2,394,198, 2,438,716, 2,440,110 and 2,440,206.

It is well known that emulsions of the type which are used in the graphic arts industry must be highly hardened to withstand the drastic conditions employed in their processing. Formaldehyde glyoxal, mucochloric acid, mucobromic acid and other organic hardening agents of the type known in the photographic art have been found suitable. In this type of hardening, an excess of hardener is used in combination with phenol, resorcinol or resorcinol aldehydes as described in U.S. Patent 2,553,506.

The following examples serve to illustrate the invention, but it is to be understood that the invention is not to be restricted thereto.

At a temperature of 70 C., parts II and III are added simultaneously over a period of one to two minutes. After the addition is completed, 175 grams of dry gelatin iS added and the whole mixture is digested for 30 minutes. The emulsion is chilled, shredded and washed in running water to conductivity of 2000 to 2500 106 ohms-1. The emulsion is reliquied at 40 C. and is then ripened at 55 for 1 hour to permit the attainment of optimum sensitivity. The above emulsion contains mole percent of silver chloride and 20 mole percent of silver bromide.

Prior to coating, the emulsion was divided into one kilogram portion and the following coating linals were added to the several emulsion batches. The amounts stated are those used for one kilogram of liquid emulsion:

To the emulsion were also added increasing amounts of the reaction product of lauryl alcohol and 35 moles of ethylene oxide prepared in accordance with the method described in U.S. Patent 1,970,578.

The emulsion batches were then coated onto cellulose acetate flmbase. After exposure in a Type IIB Sensitometer, the exposed films were developed for three minutes in the following lithographie developer which is described in the Ansco Graphic Arts Handbook, p. 38 (1958):

Water 1iters 2.0 Sodium sulfite, anhydrous grams 120.0 Paraformaldehyde do 30.0 Potassium metabisulte do 10.5 Boric acid (crystals) do 30.0 Hydroquinone do 90.0 Potassium bromide do 6.0 Water to make 4.0 liters.

The solution was allowed to remain for 2 hours in a stoppered container before use -to permit the formation of formaldehyde bisulfite. t.

The developed films were short-stopped; fixed and washed. The plotted sensitometric curves had a much steeper gradation than those of a typ emulsion which had been prepared without the use of the high molecular weight polyoxyethylene lauryl ether.

The results obtained are further illustrated by curves A to F of FIGURE l of the accompanying drawing. The identification of the curves and the amounts of additive employed are as follows. *Y

Curve: Amounts (mg./ kg. emulsion) A 0.0 B 40.0 C 100.0 D 200.0 E 400.0 F 1000.0

Curve MQ is the characteristic curve of samples A to F when developed in an Ansco Developer A-47, a commercially available metal hydroquinone developer which contains a large amount of uncombined sodium sulfte. The formula of this developer is published on p. 37 of the Ansco Graphic Handbook.

EXAMPLE n Example I was repeated with the exception that the polyoxyethylene lauryl ether was replaced by increasing amounts of the reaction product of phthaloyl chloride and polyethylene glycol (molecular weight=6000) prepared according to the method described in U.S. Patent 2,567,076. This polymer has the following probable for- The emulsion batches were then coated onto a polycarbonate iilmbase. After drying and exposure in a Type IIB Sensitometer, the exposed film was developed for 3 minutes in the following developer solution:

Water to make 1 liter.

The developed film samples were short-stopped, processed, washed and dried. A plotting of their curves is shown by FIGURE 2 of the accompanying drawing. The identification of the curves and of the amounts of additive employed are as follows. v

6 Amounts (mg./ kg. emulsion) 0.0 40.0 100.0 200.0 400.0 1000.0

EXAMPLE III Example I was repeated with the exception that the lauryl polyoxyethylene ether was replaced by corresponding amounts of the commercially available product Carbowax 6000, a polyoxyethylene glycol having an average molecular weight of 6000. The results were essentially identical with those described in Example I.

EXAMPLE IV The polyoxyethylene lauryl ether was replaced by the commercially available product Polyoxy WSR-35, a polyoxyethylene glycol possessing a molecular weight of several hundred thousand. The results obtained were essentially identical to those described in Example I.

EXAMPLE V Example I was repeated with the exception that the polyoxyethylene lauryl ether additions were made during the ripening stage of the emulsion preparation and that the coating finals solution was devoid of such additives. The results obtained were identical to those described in Example I.

While the present invention has been described with reference to certain preferred procedures, it is evident that the invention is not limited thereto, that variations may be made to the procedures described therein, and that equivalent materials may be substituted without departing from the scope of the invention. For instance, silver chloride and silver chlorobromoiodide emulsions can be used in place of the silver chlorobromide emulsions illustrated in the examples. In place of the specific polyoxyalkylenes illustrated by the examples, other polyoxyalkylene derivatives of high molecular weight can be used lwith similar results. Synthetic colloidal carrier materials such as polyvinyl alcohol or partially hydrolyzed polyvinyl acetate can be used in place of gelatin. Special sensitizing agents which are known to the art can be added to the emulsions to increase their inherent speed, particularly such sensitizing agents which render the emulsion more sensitive to the blue, green and red regions of the spectrum. In place of saponin, synthetic surfactants or wetting agents such as isopropylnaphthalene sulfonic `acid or other cationic, anionic and non-ionic wetting agents can be used which aid in the preparation of even coatings without bubble formation, provided they do not have any deleterious effect on the photographic properties of the emulsions. In place of the cellulose ester and polycarbonate filmbase, other film supports such as polystyrene or polyvinyl chloride-polyvinyl acetate may be used.

It will be understood, therefore, that I contemplate as included within my invention all modifications and equivalents falling within the scope of the appended claims.

I Claim:

1. A photographic film comprising a base and a lightsensitive silver halide emulsion of the type suitable for half-tone reproduction, said emulsion having a gamma higher than 8.0, said silver halide being selected from the group consisting of silver chloride, silver chlorobromide,

and silver chlorobromoodide, said emulsion containing a dicarboxylic acid ester of a polyethylene glycol which glycol has an average molecular weight of 4000 to 9000, said ester having a molecular weight of at least 29,000 and being present in a concentration ranging from l0 to 1000 milligrams per 100 grams of silver halide present in the preparation of the emulsion.

2. A photographic lm according to claim 1, wherein the silver halide content corresponds to 2-10 grams of References Cited UNITED STATES PATENTS 1,970,578 8/1934 Schoeller et al. 260-98 NORMAN G. TORCHIN, Primary Examiner metallic silver per square meter of coated area, and the 10 CAROLYN E. DAVIS, Assistant Examiner content of said -polymeric ester ranges from 1 to 100 milligrams per square meter of coated area.

3. A photographic lm according to claim 1 wherein said film is orthochromatically sensitized.

U.S. Cl. X.R. 96-66.3

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