US3167430A

US3167430A - Production of photographic silver halide emulsions

Info

Publication number: US3167430A
Application number: US4625A
Authority: US
Inventors: Lohmer Karl; Kolb Gunter
Original assignee: Agfa AG
Current assignee: Agfa Gevaert NV
Priority date: 1959-01-27
Filing date: 1960-01-26
Publication date: 1965-01-26
Anticipated expiration: 1982-01-26
Also published as: GB902891A; CH389399A; BE586983A; DE1202132B; FR1248730A

Description

3,ld7,43il PRGDUCTEGIN fil PEHE'EGQRAPHIQ SELVER HALlDE EM LSlGNS Karl Lohnrer, Leverlrusen, and Gunter Kelli, tCologne- Stammheim, Germany, assignors to Agla Alrtiengeseilschaft, Leverkusen, Germany, a corporation of Germany No Drawing. Filed Jan. 26, 1959, Ser. No. 4,625 Claims priority, applicatioinfitirmany, Jan. 27, 1959,

2 Qiainss. (Cl. Q-lld) The invention relates to the production of photographic silver halide emulsions.

Usually, silver halide emulsions are prepared by combining aqueous solutions of silver nitrate and awatersoluble halide in the presence of a protective colloid whereby silver halide is precipitated. The purpose of the protective colloid during the precipitation is to prevent the agglomeration of the silver halide grains, to iniluence the grain distribution and to control the growth of the grain and also the formation of sensitivity centres during the physical and chemical ripening.

For a long time, gelatinhas proved particularly suitable in practice as a protective colloid. It largely satisfies the photographic technical requirements which are demanded of a protective colloid. On the other hand, it does however have certain disadvantages, since it is a natural product, so that it is subject to certain fluctuations as regards quality and consequently shows changing photographic properties, which in certain circumstances cannot be detected during the processing operations, even with highly developed testing methods. Moreover, it has the disadvantage that it is attacked by bacteria and is subject to a chemical degradation by hydrolysis during the manufacture and storage of the emulsions. Consequently, numerous proposals have already been made for replacing the gelatin by synthetic products, such for example as polyvinyl alcohol, polyvinyl acetals, cellulose derivatives, polysaccharide derivatives, polycarboxylic acids and polycarboxylic acid amides.

It is known from United States Patent No. 1,981,102 to employ polyacrylic acid or other polymeric carboxylic acids as a binder for photographic layers.

According to United States Patent No. 2,632,794, copolymers of acrylamide, acrylic or methacrylic acids and acrylonitrile or methyl and vinyl ketones are used as dispersing agents for silver halide during the preparation of photographic emulsions.

According to German patent specification No. 1,040,- 370, highly polymeric substances with a predominant proportion of acid and nitrile groups, more especially copolymers of acrylic acid and acrylonitrile, are recommended as binders for photographic layers. If necessary, these polymers can comprise a small proportion of acrylamide or vinyl alcohol units. In spite of the many proposals, the replacement of gelatin by synthetic substances has only been partially successful, since many plastics do not have, to the same degree as gelatin, the protective colloid properties which are necessary photographically, such as for example control of the grain size during the precipitation and physical ripening and prevention of the agglomeration of the silver halide grains. Other plastics are only capable of limited use because they produce insoluble deposits with the aqueous solution of the silver nitrate.

It has now been found that these disadvantages can be avoided and silver halide emulsions which are exccllently suitable from a photographic point of view can be obtained by using, as protective colloid in the precipitation of the silver halide, film-forming copolymers of 60 to 98% by weight of methacrylamide and/or acryl- United States Patent l Patented Jan. 26, 132%5 amide, l to 38% by weight of an ester of acrylic acid or methacrylic acid with a monohydric saturated alcohol which contain 1 to 20, preferably 1 to 10 carbon atoms and/or a vinyl ester of a saturated aliphatic monocarboxylic acid with 1 to 20 carbon atoms and 1 to 24% of an olcfinically unsaturated organic compound containing acid groups.

By the term saturated alcohols is to be understood alcohols which are devoid of nonbenzenoid unsaturation, i.e., and aliphatic, cycloaliphatic, araliphatic alcohols. Especially suitable are copolymers of 65 to by Weight of methacrylamide and/or acrylamide, 5 to 34% by weight of the aforementioned ester and 1 to 15% by Weight of an olefinically unsaturated organic compound containing acid groups.

Examples of alcohols used for acrylic or methacrylic acid are:

Methyl alcohol, ethyl alcohol, isopropyl alcohol, n-butyl alcohol, isononyl alcohol, cetyl alcohol, cyclohexyl alcohol, benzyl alcohol. As examples of the vinyl esters of a saturated aliphatic carboxylic acid with 1 to 20 carbons, there are mentioned: vinyl acetate, vinyl propionate, vinyl butyrate and vinyl stearatec; Examples of olefinically unsaturated organic compounds containing acid groups are more especially those olefinically'unsaturated compounds which contain carboxylic, sulphonic or preparing the ester of phosphoric acid groups, such as acrylic acid, methacrylic acid, sorbic acid, maleic acid, fumaric acid, itaconic acid, citraconic acid, as well as their semi-esters with the above cited alcohols, vinyl sulphonic acid, styrene sulphonic acid, vinyl phosphonic acid and others.

The protective colloids used according to the invention are prepared by known polymerization methods, and preferably by polymerization in Water in the presence of watersoluble radical formers. The aqueous .polymer solutions thus obtained can be directly used asa protective colloid solution.

It was surprising to find that the silver halide emulsions prepared in the presence of the protective colloidsaccording to the invention do not have the disadvantages referred to above. They have important advantages over the silver halide emulsions prepared with known protective colloids. For example, the aqueous solutions or emulsions of the copolymers according to the invention are stable at all pH values which are to be considered practically and do not produce with aqueous silver nitrate solutions any deposit which could disturb the processing. The copolymers are excellent film formers which can for example be cross-linked with formaldehyde and yield elastic films. They are compatible with gelatin and ot er natural or synthetic protective colloids, such as polyvinyl alcohol, polycarboxylic acid amides or polycarboxylic acids, and consequently can also be used in combination therewith. The silver halide emulsions prepared with the protective colloids according to the invention can be quickly and quantitatively coagulated at pH values from 3 to 4, freed from the excess salts by a washing process, and thereafter the coagulate can easily be redispersed again by raising and lowering the pH value. The absolute concentration of the silver halide and also the ratio between protective colloid and silver halide can be varied within wide limits, and very highly sensitive silver halide emulsions are obtained with an extremely fine grain. The photographic materials prepared with the aid of the silver halide emulsions according to the invention are non-fogging and are distinguished by particularly good keeping qualities, even under unfavorable atmosphcric conditions.

For the preparation of the silver halide emulsions, the aqueous solutions or emulsions of the protective colloid according to the invention are supplied and the aqueous solutions of the silver salt and Water-soluble halide are sibly with the addition of other photographic auxiliaries.

The further processing step takes place in accordance with known processes.

In the following examples the parts indicated are parts by Weight.

Example I 695 parts of water are placed in a stirrer-type vessel and 72.5 parts of methacrylamide, 25 parts of a a ueous solution of acrylamide, 22.5 parts of methyl acrylate and 2.5 parts of methacrylic acid are introduced 7 ,and homogeneously mixed while passing nitrogen over the mixture. The mixture is then heated to 75- C. and polymerized by adding 0.3 part of potassium persulphate. After 8 hours, the viscosity has risen considerably and a substantially 12% polymer solution is obtained.

19 parts of potassium bromide and 0.5 part of potassium iodide are now added to a solution of 400 parts of "Water and 100 parts of the copolymer solution and themixture is heated to 40 C. A cold solution of parts of silver nitrate dissolved in 150 parts of Water,

to which had been added 25 parts of ammonia water with a density of 0.91, is then poured into the said mixture "over a period of 1 minute. The mixture is digested for minutes at C. and'coagulation is thereafter effected by adding 52 parts of dilute sulfuric acid (density The supernatant salt solution is decanted off, 7 the coagulate is washed twice with 1000 parts of water and is finally redispersed in 200 par-ts of water to which 1 part of sodium carbonate had been added.

It is immediately subjected, with the addition of 30 g. of gelatin, to a chemical ripening at C. for to 80 minutes. 011 completing the ripening, the emulsion is cast by known methods on to a layer support.

Example 2 As described in Example 1, 620 parts of water are provided and'40 parts of methacrylamide, 310 parts of a 10% aqueous solution of acrylamide, 25 parts of vinyl acetate and Sparts of a 50% aqueous solution of acrylic acid are introduced and polymerization carried out as described therein. A substantially 10% aqueous polymer 3 solution is obtained.

The processing to form photographic silver halide emulsion layers takes place as described in Example 1.

Example 3 As described in Example 1, 716 parts of water are provided and 78 parts of methacrylamide, 15 parts of ethyl acrylate, 3 parts of vinyl propionate and 8 parts 'of a 50% aqueous solution of acrylic acid are introduced and polme'rization takes place as described therein. A substantially 12% aqueous polymer solution is obtained.

The processing to form photographic silves halide emulsion layers takes place as described in Example 1.

Example 4 are now simultaneously poured within 5 minutes at C. into a solution of 50 parts of the copolymer solution in 300 parts of water. The emulsion is thereafter subjected to a physical ripening for 30 minutes, and after adding parts of gelatin with a powerful ripening action, chemical ripening takes place at the same temperature over a period lasting 30 minutes. The emulsion is then cooled, provided with the necessary casting additives, such as optical sensitizer, wetting agent and hardening agent and cast. The gelatin can also be replaced by another'carrier colloid to which has been added the necessary quantity of chemical sensitizers.

Example 5 As described in Example 1, 716 parts of water are provided and 79.5 parts of methacrylamide, 165 parts of ethyl acrylate and 8 parts of a 50% aqueous solution of acrylic acid are introduced and polymerization is peracid are added, the silver halide coagulating and settling very quickly. The precipitate is freed from the supernatant salt solution, washed several times with slightly acidified water, again redispersed with dilute sodium hyocyanate, thiosinamine, and sodium thiosulphateu After completing the ripening, the emulsion is cast by known 1 methods on to a supporting layer.

We claim:

1. In av process for the production of photographic silver halide emulsions by precipitating a silver halide in an aqueous medium containing a protective colloid, coagulating said emulsion to obtain a coagulate containing said protective colloid and said precipitated silver halide and redispersing said coagulate, the improvement according to which the silverhalide is precipitated in an aqueous medium containing as the only protective colloid a film-forming copolymer consisting essentially of (1) 65 to by weight of a member of the group consisting of methacrylamide, acrylamide and mixture thereof, (2) 5 to 34% by weight of a monomer of the group consisting of vinyl esters of a saturated aliphatic monocarboxylic acids containing from 1 to 20 carbon atoms, esters of acids of the group consisting of acrylic acid and methacrylic acid with monohydric saturated alcohols containing from 1 to 20 carbon atoms and (3) 1 to 15% by weight of an olefinically unsaturated organic compound containing acid groups selected from the group consisting of acrylic acid, methacrylic acid, sorbic acid, maleic acid, fumaric acid, itaconic acid, citraconic acid, vinyl sulfonic acid, styrene sulfonic acid and vinyl phosphonic acid.

2. A process as defined in claim 1, in which the filmforming copolymer is a copolymer formed from approximately 72.5 parts of methacrylamide, 2.5 parts of acry1- amide, 22.5 parts of methyl acrylate, and 2.5 parts of methacrylic acid, all parts being by weight.

References Cited in the file of this patent UNITED STATES PATENTS 2,461,023 Barnes et a1. Feb. 8, 1949 2,611,763 Jones Sept. 23, 1952 2,811,494 Smith et a1 Oct. 29, 1957