NO123330B - - Google Patents

Description

Method of sensitizing a

photographic silver halide emulsion.

Q

The present invention relates to a method for sensitizing a photographic solvohalide emulsion with a noble metal sensitizing compound and labile selenium.

In the U.S. patent no. 3 297 44-6 describes a method for sensitizing photographic systems, where a noble metal sensitizing compound and "labile selenium" are used, and the term "labile selenium" refers in this connection to both colloidal selenium and to selenium in a selenium compound capable of reacting at room temperature (20°C) with solv nitrate in aqueous solution to form water-insoluble solv selenide. Such a compound will hereinafter be termed a "labile selenium compound". The precious metal sensitizing compound and labile selenium produces a synergistic effect.

The procedure in the above-mentioned US patent is applicable in

a number of precious metal sensitizable photographic systems, and is particularly useful for sensitizing photographic solvent halide emulsions. However, sensitization by this method is not in all cases as easily adjustable as is desirable.

It has now been discovered that it is possible to convert a non-labile selenium compound into labile selenium in situ, and consequently possible to sensitize a precious metal-sensitizable photographic system by incorporating into this a noble metal sensitizing compound and a non-labile selenium compound and activating the latter, so that labile selenium is provided.

According to the present invention, it is thus provided

a method for sensitizing a photographic solvent halide emulsion with a noble metal sensitizing compound and labile selenium, characterized in that the labile selenium is formed in situ by activating a non-labile selenium compound.

A major advantage of using the sensitizing method according to the present invention is that the sensitizing of the photographic emulsion can be easily regulated. The sensitization can occur at any time it is desired to activate the non-labile selenium compound. The degree of sensitization can also be regulated by varying the intensity

on activation. With the sensitizing according to the present invention, a photographic solvent halide emulsion with a predetermined sensitivity can thus be produced.

Any method of activating non-labile selenium compounds can be used in the present invention as long as they make the selenium compounds labile, the preferred method of activating non-labile selenium compounds to make them labile is to use reducing compounds. Another preferred method is to use a higher molar concentration of the noble metal compound than of the non-labile selenium compound. A third preferred method of

way is to heat the non-labile selenium compound in the system after the latter has been sensitized by heating in the presence of the noble metal sensitizing compound.

Non-labile selenium compounds that can be used in the present invention include e.g. potassium selenicyanate, selenic acid, inorganic., isoselenicyanate complexes, etc.

The concentration of the non-labile selenium compound, which

is to be activated for the production of labile selenium in situ, can be varied considerably depending on the particular non-labile selenium compound

etc. used, the composition of the photographic emulsion, the amount of precious metal sensitizing agent and its chemical composition, etc.

It has been found that useful results can be obtained when using amounts as small as 0.05 mg of the non-labile selenium compound per mole of silver halide, although considerably larger amounts, e.g., from 5.0 mg or more per mole of silver halide, can also be used .

The noble metal sensitizing compounds that can be used in the present invention include well-known gold sensitizing compounds and other noble metals such as e.g. palladium, platinum and any of those described in US Patent No. 2,448,060. Typical and very suitable gold sensitizing compounds are described in US

Patent No. 2,399,083 and US Patent No. 2,642,361.

■ Illustrative examples of noble metal sensitizing compounds that can be used in the present invention include f Saying: gold chloride,

potassium aurate,

potassium uric acid,

potassium auricyanide,

potassium aurithiocyanate,

gold sulfide,

gold selenide,

gold iodide,

potassium chloride,

ethylenediamine bis-gold chloride,

ammonium chloroplatinate, i.e. (NH^^PtCl^,

ammonium chloropalladate, i.e. (NH^igPdClg, and the complex organic gold sensitizing compounds designated I through X in US Patent No. 2,642,361. Triphenyl phosphate gold (I) chloride can and-

is used, as the gold ion here acts as the noble metal sensitizing compound while triphenyl phosphate activates the non-labile selenium compound.

The concentration of the noble metal sensitizing compound is best determined purely experimentally, and it depends on the method chosen for activating the non-labile selenium compound, the system in question, as well as the selected noble metal sensitizing compound.

otherwise. When an aluminum halide system is to be sensitized with a gold-sensitizing compound, and the non-labile selenium compound is to activate

res with a reducing agent, then usually from 0.1 to 5-0 mg of the gold sensitizing compound per mole of solvate halide will be well suited,

and a similar concentration is also appropriate in those cases where act-

the proofing is carried out by heating the non-labile compound in the gold-sensitized system. If the activation is carried out by means of a relatively high molar concentration of the noble metal sensitizing compound, then the concentration should be at least 2 mol of the noble metal compound per mol of the non-labile selenium compound. The noble metal sensitizing compound should preferably be used in a concentration varying from 4-5 to 10 mol per mol of the non-labile selenium compound, although concentrations up to 15 mol per mol of non-labile selenium compound can also be used. If the concentration of the noble metal sensitizing compound is less than 2 moles per mole of the non-labile selenium compound, then the latter compound will not be sufficiently activated to produce a synergistic sensitizing effect.

A preferred method for activating non-labile selenium compounds is, as mentioned earlier, by using a reducing agent. One can use any reducing agent that is effective for the stated purpose. Among the reducing agents that can be used are benzothiazolium salts such as benzothiazole methiodide, benzothiazole methbromide, 2-hydroxymethyl-benzothiazoleethyl iodide, 2-hydroxymethyl-benzothiazole methiodide, etc, mercaptans such as 2-mercaptobenzoic acid, thiolactic acid, 2-mercapto-benzothiazole, etc., disulfides such as e.g. diphenyldisulfide, triphenylphosphine, stannous chloride, benzothiazoline compounds such as 3-methyl-benzothiazoline, 2-methyl-3-methyl-benzothiazoline, 2,2-dimethyl-3-methyl-benzothiazoline, etc., alkali metal sulphites such as potassium sulphite, sodium sulphite, etc.

The reducing agent can be directly added to the sensitizing mixture and reacted with the non-labile selenium compound to form labile selenium in the photographic system, or it can be added to the photographic system, e.g. a solvent halide emulsion, after the sensitizer has been added to form labile selenium in situ. If it is desired, the reducing agent can also be previously incorporated into the gelatin in a solvent halide emulsion. The concentration of the reducing agent can of course vary greatly, all depending on the particular non-labile selenium compound used, its concentration, the photographic emulsion composition, etc. There should preferably be a stoichiometric excess of the reducing agent in relation to the non-labile selenium compound to be reduced. Suitable concentrations include e.g. from 1 to 50 mg P©r solvmol.

When the non-labile selenium compound is activated by heating, the temperature and heating time may vary significantly, depending on the photographic solvohalide emulsion composition, the concentration of the non-labile selenium compound, the concentration of the noble metal compound, etc., and it has been found satisfactory to vary each step from 55 ° to 70°C i' from 20 minutes to 100 minutes.

Particularly favorable results are obtained when the sensitizing mixture contains a water-soluble thiocyanate compound. Typical thiocyanates in this connection include sodium thiocyanate, potassium thiocyanate, ammonium thiocyanate, etc. The amount of the thiocyanate compound used will vary depending on the particular system to be sensitized, the relative amounts of the sensitizing compounds, etc.

The sensitizing additives, i.e. the noble metal sensitizing compound, the non-labile selenium compound and the reducing agent, can be added to the photographic emulsion in different ways and at different stages of its preparation. For the solvent halide emulsion, such additives can thus be added with usable effects after Ostwald ripening and for one or more of the final processing steps. The solvohalide emulsion is preferably added to the above-mentioned sensitizing compounds after the solvohalide grains have essentially acquired their final size and shape. Said additives can be added in the form of their aqueous solutions, in cases where they are soluble in water, or in a harmless organic solvent in cases where the sensitizing compounds do not have sufficient solubility in water to form an aqueous solution. Particularly usable organic solvents include ethanol, methanol, pyridine, acetone, dioxane, etc. In this connection, organic solvents with a relatively high polarity are preferred. In those cases where it is desirable to add the sensitizing compounds in a form other than a solution, this can also be done, especially when the sensitizing compounds are available in the form of a colloidal suspension. In certain cases, it is possible to add the sensitizing compounds suspended in an organic solvent which forms very small suspended particles in the photographic emulsion, thereby obtaining colloidal particles of the same type as are found in coupling dispersions. Dispersing media that can be used for the above purposes include tricresyl phosphate, dibutyl phthalate, triphenyl phosphate, etc.

Vacuum-deposited photographic solvent halide emulsions which are essentially free of common solvents, binders or dispersants can also be sensitized according to the present invention by incorporating the sensitizing compounds into a coating or layer that is in contact with the vacuum-deposited, light-sensitive material. Suitable vacuum-deposited solvent halide systems that can be sensitized accordingly

present invention, is described in Canadian patent no. 790 005,

US Patent No. 3,384,490 and Belgian Patent No. 639,020.

The solvent halide emulsion in one photographic element which can be sensitized according to the present invention can also contain common additives such as gelatin softening agents, spreading agents, anti-haze agents such as e.g. azaindines, as well as hardeners such as aldehyde hardeners, e.g. formaldehyde, mucochloric acid, glutaraldehyde bis(sodium bisulfite), maleic acid dialdehyde, aziridines, dioxane derivatives and oxypolysaccharides. These additives can be added to the emulsion before or after sensitizing dyes, if such are used. Sensitizing dyes that can be used for sensitizing such emulsions are e.g. described in US patent no. 2,526,632 and no. 2,503,776. Spectral sensitizing compounds that can be used are e.g. cyanines, mero-cyanines, complex (trinuclear) cyanines, complex (trinuclear) mero-cyanines, styryls and hemicyanines. Antifreeze compounds can also be incorporated into the solvohalide emulsion if this is desired, or these can be in a separate substrate. Different solar salts can be used as the sensible salt, e.g. solv bromide, solv iodide, solv chloride or mixed solv halides such as solv chlorobromide or solv bromo iodide.

The solvent halide emulsion layer in a photographic element which

can be sensitized according to the present invention, can contain any hydrophilic water-permeable binder suitable for this purpose. Suitable compounds include gelatin, colloidal albumin, polyvinyl compounds, cellulose derivatives, acrylamide polymers, etc. Mixtures of these binders can also be used. The binder for the emulsion layer in the photographic element may also contain dispersed polymerized vinyl compounds. Such compounds are e.g. described in US patents No. 3,142,568, No. 3,193,386, No. 3,062,673 and No. 3,220,844, and includes water-soluble polymers of alkyl acrylates and methacrylates, acrylic acid, sulfoalkyl acrylates or methacrylates and the like.

The solvent halide emulsion in a photographic element which can be sensitized according to the present invention can be applied to a wide range of substrates. Typical substrates are cellulose film, cellulose ether film, polyvinyl acetate film, polystyrene film, poly(ethylene terephthalate) film and similar films or resinous material in addition to glass, paper, metal and the like. As examples of paper coated with an α-olefinic polymer, and especially polymers etc. cc-olefins containing two or more carbonate atoms, one can mention paper coated with polyethylene, polypropylene, ethylene butane k-opolymer and the like.

It has been found that the speed of photographic emulsions sensitized according to the present invention can be further increased by incorporating a number of hydrophilic colloids in the emulsions, such as e.g. carboxymethyl protein of the type described in US Patent No. 3 Oll 890 and polysaccharides of the type described in Canadian Patent No. 635,206.

Photographic emulsions sensitized according to the present invention may also contain speed-increasing compounds such as e.g. quaternary ammonium compounds, polyethylene glycols or thioethers. Useful effects can very often be obtained when the aforementioned speed-increasing compounds are added to the photographic developer solutions instead of or in addition to the photographic emulsions.

Photographic elements that have been sensitized according to the present invention can be stabilized with labile sulfur compounds, as described in US patent no. 3,297,447. These labile sulfur compounds are particularly effective for controlling opacity in the film without having harmful effects on the speed of the stabilized photographic system. Particularly useful labile sulfur compounds include water-soluble thiosulphates such as e.g. alkali metal thiosulphates, including sodium and potassium thiosulphate, as well as ammonium thiosulphate, thioureas such as e.g. thiourea, allylisothiourea, diacetylthiourea, thiosemicarbazide, thiocarbamates such as isopropylthiocarbamate, etc.

The amount of the labile sulfur compound used to stabilize photographic systems sensitized according to the present invention can vary considerably depending on the particular sensitized photographic system used, processing conditions, including temperature and time for post-aging, etc. Particularly useful results have been obtained with concentrations varying from 0.1 to 10 mg per mol of solvent halide. Larger and smaller amounts can, however, be used without this damaging the sensitometric properties of the photographic system, the rien or the labile sulfur compounds should preferably be added during the chemical sensitization of the photographic system.

Test for labile and non-labile selenium.

F,n 0.1N aqueous solution of silver nitrate is added to an aqueous solution or suspension of the compound to be tested. If a black precipitate of sol selenide is obtained, then labile selenium is present.

Examples of this sample are the following.

10 ml of distilled water in a prover were added to 6 mg of potassium

c

Selenium cyanate. This solution was then added approx. 5 ml of 0.1N silver nitrate. No silver selenide was formed, indicating that potassium selenium cyanate is a non-labile selenium compound. 6 mg of potassium selenium cyanate was added to 10 ml of distilled water in a test tube. When 1.0 ml of a 10 mg per ml solution of potassium chloroaurate was added to 1.0 ml of potassium selenide cyanate solution, the solution turned red. This red solution was then added approx. 5 ml of a 0.1N silver nitrate solution. A black precipitate (silver selenide) immediately formed, while the supernatant became colourless. This indicates that potassium selenocyanate becomes labile in the presence of a high concentration of a gold sensitizing compound.

Selenic acid (13 mg) was dissolved in 10 ml of water, and to this solution was added, while stirring, 375 mg of tetrakis (triphenylphosphine) platinum /-(CgHc-)^/^ Z~^t_7 dissolved in 100 ml of benzene. When slightly heated to approx. 60 C, the mixture turned red. To the solution was added 6 ml of a 0.1N aqueous silver nitrate solution, and a black precipitate formed. This indicates that selenic acid is activated by the platinum compound, whereby labile selenium is provided.

The invention is illustrated by the following examples.

Example 1. Activation using reducing agents.

A silver bromoiodide emulsion was prepared with a medium grain size and which contained 3-4 mole percent iodide. A first portion of the emulsion was chemically sensitized by adding 2 mg of potassium chloroaurate per mole of silver, 100 mg of potassium thiocyanate per mole of silver and 1.6 mg of potassium selenocyanate per mole of silver. The emulsion was then heated for 4-0 minutes at 65°C.

Another portion of the emulsion was sensitized in the same way as with the first-mentioned portion, but with the addition of 10.1 mg of benzothiazole methiodide per mole of silver and then heating for 9 minutes at 65°C.

A third portion of the emulsion was sensitized in the same way as described in the first paragraph, except that 8.2 mg of benzothiazole metbromide per mole of silver was added and heated for 9 minutes at 65°C.

A fourth portion of the emulsion was sensitized in the same way as for the first portion, except that 11.7 mg of 2-hydroxymethylbenzothiazoleethyl iodide per mole of silver was added and heated for 12 minutes at 65°C

These emulsions were then applied to a substrate of cellulose acetate with a degree of coverage of 58.2 mg silver per dm o. The films were then exposed in a sensitometer with an intensity scale, developed for 5 minutes in a Kodak developer <n>DK-50w, fixed, washed and dried. The following results were obtained.

This example shows that the reducing agents activate potassium selenocyanate so that it becomes labile with a rate increase of up to 14-0$. Example 2. Activation by other reducing agents.

A first portion of the emulsion from example 1 was chemically sensitized with 2 mg of potassium chloroaurate per silver mole, 100 mg potassium thiocyanate per moles of silver and 1.6 mg of potassium selenium cyanate per silver mol. The sensitized emulsion was then heated for 40 minutes at 65°C.

Another portion of the emulsion was chemically sensitized with 4 mg of potassium chloraurate per silver mole, 100 mg potassium thiocyanate per mole of silver, 1.6

mg potassium selenocyanate per silver mole and 20.2 mg benzothiazole methiodide per silver mol. This portion was then heated for 15 minutes at 65°C.

A third portion of the emulsion was sensitized in the same way as for the second portion, except that the benzothiazolium salt was replaced with 3>4 mg of 2-mercaptobenzoic acid per silver moles, and that heating was used for 20 minutes at 65°C.

These emulsions were then coated and treated in the same way as described in example 1. The following results were obtained.

Example 3. Activation by reducing agents in the absence of a precious metal.

A first portion of the emulsion from example 1 was chemically sensitized with 100 mg of potassium thiocyanate per moles of silver and 1.6 mg of potassium selenium cyanate per silver mol. The emulsion was then heated for 30 minutes at 60°C.

Another portion of the emulsion was sensitized in the same way as for the first portion, except that 2.8 mg of triphenylphosphine was added per silver mole and heated for 6 minutes at 60°C.

A third portion of the emulsion was sensitized in the same way as for the first portion, except that 10.1 mg of benzothiazi methiodide was added per silver mole and heated for 20 minutes at 60°C.

These emulsions were then coated and treated in the same manner as described in Example 1. The following results were obtained.

This example shows that the reducing agents convert a non-labile selenium compound into a labile selenium compound, which is an effective se sitivating agent.

Example 4. The ratio between labile selenium sensitizers and activated non-labile selenium compounds.

A first portion of the emulsion from example 1 was chemically sensitized with 2 mg of potassium chloroaurate per silver mole, 100 mg potassium thiocyanate per

■ silver mole and 0.8 mg N,N-dimethylselenorea per silver mol. The sensitized emulsion was then heated for 15 minutes at 65°C.

Another portion of the emulsion was chemically sensitized with 4 mg of potassium chloraurate per silver mole, 100 mg potassium thiocyanate per mole of silver, 1.6 mg of potassium selenium cyanate per moles of silver and 20.2 rag benzothiazole methiodide per silver mol. This portion of the emulsion was also heated for 15 minutes at -65°C

These emulsions were then coated and treated as described in

example 1.

The following results were obtained.

This example shows that non-labile compounds which are activated by means of reducing agents are equivalent to labile selenium compounds with regard to sensitizing effect.

Example 5. The relationship between labile selenium sensitizers and activated non-labile selenium compounds.

A first portion of the emulsion from example 1 was chemically sensitized with 100 mg of potassium thiocyanate per silver mole and 0.8 mg N,N-dimethylsele urea per silver mol. The emulsion was then heated for 9 minutes at 60°C. Another portion of the emulsion was sensitized with 100 mg of potassium thiocyanate per sSlvmol, 1.6 mg of potassium selencyanate per sSlvmol and 1.4 mg of triphenylphosphine per sSlvmol. This emulsion was then heated for 6 minutes at 60°C.

The emulsions were then strained and treated as described in Example 1. The following results were obtained.

Example 6. The effect of a reducing agent together with a non-labile selenium compound..

A first portion of the emulsion from example 1 was sensitized with 100 mg of potassium thiocyanate per solvmol and 2.8 mg of triphenylphosphine per solvmol. The emulsion was then heated for 30 minutes at 60°C.

Another portion of the emulsion was sensitized with 100 mg potassium thiocyanate per sSlvmol and 1.6 mg potassium selenocyanate per sSlvmol and then heated for 30 minutes at 60°C.

A third portion of the emulsion was sensitized in the same way as the first portion, but with the addition of 1.6 mg of potassium selencyanate per sSlvmol and heating for 6 minutes at 60°C.

These emulsions were applied and treated as described in example 1. The following results were obtained.

This example illustrates the synergistic effect achieved when a reducing agent is combined with a non-labile selenium compound. One achieves a speed increase of 1000$.

Example 7» The effect of reducing agents on labile selenium compounds.

A first portion of the emulsion from example 1 was chemically sensitized with 2 mg potassium chloroaurate per sSlvmol, 100 mg potassium thiocyanate per solvmol and 0.8 mg N,N-dimethylselenorea per sSlvmol. The emulsion was then heated for 15 minutes at 65°C.

Another portion of the emulsion was sensitized in the same way as for the first portion, except that 10.1 mg of benzothiazole methiodide per sSlvmol was added. This second portion was then heated for 30 minutes at 65°C.

These emulsions were then coated and treated as described in example 1. The following results were obtained.

This example shows that reducing agents have no effect on selenium compounds, which are already labile fN,N-dimethylselenorea is indicated as labile in the previously filed patent application no. 468 972. Example 8 Comparison between activated non-labile selenium compounds and common sensitizers.

An emulsion of the same type as described in example 1 was prepared and sensitized with 2.0 mg sodium thiosulphate per solvmol and 0.75 mg potassium chloraurate per solvmol. Another portion of the emulsion was sensitized with 49 mg of selenic acid per solvmol, 94-6 mg of sodium sulphite per solvmol and 0.75 mg of potassium chloroaurate per solvmol. These emulsions were then applied and treated in the same manner as described in Example 1. The following results were obtained.

This example shows that gold and non-labile selenium compounds that have been made labile with reducing agents are better sensitizers than common sulfur and gold sensitizers.

Example 9 The action of a reducing agent and a non-labile selenium compound.

Portions of the emulsion from Example 1 were sensitized with various sensitizers as indicated below. The emulsions were then applied and treated in the same manner as described in Example 1, and the following results were obtained.

This example shows that activation of a non-labile selenium compound with a reducing agent will increase the relative velocity of an emulsion by over 1000$. This example also shows that adding a gold compound + a reducing agent to a non-labile selenium compound will increase the relative velocity of the emulsion by over $4-000. Example 10.

A first portion of an emulsion of a similar type as described

in example 1, was chemically sensitized with 4 mg of potassium chloraurate per solvmol, 100 mg sodium thiocyanate per mole of silver, 1.6 mg of potassium selenium cyanate per silver mole and 20.2 mg benzothiazole methiodide per silver moles and then heated for 15 minutes at 65°C.

Another portion of the emulsion was chemically sensitized in the same way as for the first portion, but with the addition of 4 mg of sodium thiosulphate per silver moles and a heating for 10 minutes at 60°C.

This example shows that sulfur compounds, such as sodium thiosulphate, act as stabilizing compounds by reducing the turbidity of an emulsion sensitized with gold and activated with non-labile selenium compounds.

Example 11.

A coarse-grained silver bromidoiodide emulsion containing 2.85 mol proaent iodide was prepared, and a first portion was chemically sensitized with 2 mg of gold sulphide per silver mole, 15 mg sodium thiocyanate per silver mole and 2.3 mg of potassium selencyanate per silver mol. This first portion of the emulsion bit then heated for 25 minutes at 65°C in the presence of 50 grams of an inert gelatin per silver mol.

Another portion of the emulsion was chemically sensitized and heated in the same way as described in connection with the first portion, except that 50 grams were used per silver moles of a naturally activated gelatin.

These pores were then coated and treated as described in Example 1, and the following results were obtained.

This example shows the irregularities that easily occur when potassium selencyanate is used together with precious metals as a sensitizer with different gelatins. U.S. patent 3"243"298, column 68, lines 35"*38, and British patent 861,984" page 2, lines 42-44, describe the use of potassium selen cyanate as a sensitizing agent, however, there is no description of this compound being used in combination with noble metals, or that the activation of this compound will give synergistic sensitizing results together with noble metals. It is thus clear from the above-mentioned patents that it depends on the type of gelatin used. By applying the method according to the present invention, it is possible to obtain reproducible results, which are not dependent on the particular type of gelatin used.Example 12.

A medium-grained s61v bromoiodide emulsion containing 3.4 mole percent iodide was prepared. A fourth portion of this emulsion was chemically sensitized by adding 2 mg of potassium chloroaurate per sSlvmol, 50 mg sodium thiocyanate per silver mole and 8 mg sodium thiosulphate per silver mol.

The emulsion was then heated for 10 minutes at 65°C

Another portion of the emulsion was sensitized with 24 mg of potassium chloraurate per solvmol, 100 mg sodium thiocyanate per BØUvmol and 8 mg sodium thiosulphate per silver mol. The emulsion was then heated for one minute at 70°C

A third portion of the emulsion was sensitized with 2 mg of potassium chloraurate per silver mole, 100 mg »atriu»ti»cyanate per silver mole and 0.8 mg N,N-di)«ethylselenorea per silver mol. The emulsion was then heated for 20 minutes at 65°C. f

A fourth portion of the emulsion was sensitized with 100 mg of sodium thiocyanate per moles of silver and 1.6 ag of potassium selenocyanate per silver mol. The emulsion was then heated for 30 minutes at 60°C.

A fifth portion of the emulsion was sensitized with 2 mg of potassium chloraurate per sSlvmol and 100 mg sodium thiocyanate per sSlvmol. The emulsion was then heated for 40 minutes at 65°C.

A sixth portion of the emulsion was sensitized with 24 mg of potassium chloraurate per sSlvmol and 100 mg sodium thiocyanate per sSlvmol. The emulsion was then heated for 20 minutes at 65°C.

A seventh portion of the emulsion was sensitized with 24 mg of potassium chloraurate per solvmol, 100 mg sodium thiocyanate per sSlvmol and 0.4 mg of N,N-dimethylselenorea. The emulsion was then heated for 5 minutes at 60°C.

An eighth portion of the emulsion was sensitized with 6 mg of potassium chloraurate per sSlvmol, 100 mg sodium thiocyanate per sSlvmol and 1.2 mg of potassium selenium cyanate per sSlvmol. The emulsion was then heated for 40 minutes at 70°C.

A ninth portion of the emulsion was sensitized with 24 mg of potassium chloraurate per sSlvmol, 100 mg sodium thiocyanate per sSlvmol and 1.8 rag potassium selenium cyanate per sSlvmol. The emulsion was then heated for 25 minutes at 65°C.

A tenth portion of the emulsion was sensitized with 32 mg of potassium chloraurate per sSlvmol, 100 mg sodium thiocyanate per sSlvmol and 1.8 mg of potassium selenium cyanate per sol mol. The emulsion was then heated for 20 minutes at 65°C.

An eleventh portion of the emulsion was sensitized with 24 mg of potassium chloroaurate per sSlvmol, 100 mg sodium thiocyanate per solvmol and 0.8 mg potassium selenium cyanate per sSlvmol. The emulsion was then heated for 40 minutes at 65°C.

The emulsions were then applied to a substrate of a cellulose acetate

with a degree of coverage of 540 mg sSlv per ft.p<.> The films were then exposed in a sensitometer with an intensity scale, developed for 5 minutes in a Kodak developer DK-50, fixed, washed and strengthened.

The following results were obtained.

This example shows that a larger amount of a gold sensitizer in a conventional sulfur-and-gold sensitized photographic system slows down the speed (compare second portion with first portion). This example also shows that an increasing concentration of the gold sensitizer in a mixture of this and a labile selenium compound lowers the gamma and increases the opacity (compare seventh portion with third portion). The above example also shows that a sensitization with a high gold concentration alone gives a speed increase corresponding to that found in a sulphur-and-gold sensitized photographic system, but that you get a lowering of the gamma and an increase of the opacity (compare sixth portion with first portion).

The above example further shows that when the molar ratio between the noble metal compound and the non-labile selenium compound is more than 2, the non-labile selenium compound is activated and forms a synergistic sensitizing combination with the noble metal, whereby a higher speed is obtained than with ordinary sulfur and gold sensitizers (compare eighth, ninth, tenth and eleventh portions with first portion).

Example 13.

A coarse-grained silver-bromoiodide emulsion was produced which contains held 2.85 mole percent iodide. A first portion of the emulsion was sensitized by adding 0.6 mg of potassium chloroaurate per silver mole, 45 mg sodium thiocyanate per silver mole and 4 mg sodium thiosulphate per silver mol. The emulsion was then heated for 16 minutes at 6o°C.

Another portion of the emulsion was sensitized with 4 mg of gold (I) sulphide per silver mole, 15 mg sodium thiocyanate per moles of silver and 2.3 mg of potassium selencyanate per silver mol. The emulsion was then heated for 30 minutes at 65°C.

A third portion of the emulsion was sensitized with 2 mg of gold (I) sulphide per silver mole, 15 mg sodium thiocyanate per mole of silver and 0.34 mg of potassium selenium cyanate per silver mol. The emulsion was then heated for 80 minutes at 65°C.

The emulsions were then applied to a cellulose acetate substrate with a degree of coverage of 484 mg silver per ft. The films were then exposed in a sensitometer with an intensity scale, developed for 3 minutes in an Elon hydroquinone developer, fixed, washed and dried. The following results were obtained.

The above example shows that the synergistic sensitizing effect according to the present invention is best achieved when using approx. 2 moles of a noble metal compound per mole of non-labile selenium compound. Concentrations of the noble metal compounds below this amount are not sufficient to activate the non-labile selenium compound thereby producing a synergistic sensitizing effect.

Example 14

A medium-grained silver bromoiodide emulsion containing 3-4 mole percent iodide was prepared. A first portion of this emulsion was chemically sensitized by adding 2 mg of potassium chloroaurate per solvmol, 50 mg of sodium thiocyanate per solvmol and 8 mg of sodium thiosulphate per solvmol. The emulsion was then heated for 10 minutes at 65°C.

Another portion of the emulsion was sensitized with 8 mg sodium thiosulfate per solvmol and 50 mg sodium thiocyanate per solvmol. The emulsion was then cooled to 40°C and 2 mg of potassium chloroaurate per solv mol and 50 mg of sodium thiocyanate per solv mol were added. The emulsion was then heated for 5 minutes at 60°C. -

A third portion of the emulsion was sensitized with 8 mg potassium chloroaurate per solvmol, 100 mg sodium thiocyanate per solvmol and 1.2 mg potassium selenocyanate per solvmol. The emulsion was then heated for 4-0 minutes at 70°C.

A fourth portion of the emulsion was sensitized with 8 mg of potassium chloroaurate per solvmol and 100 mg of sodium thiocyanate per solvmol. The emulsion was then heated for 40 minutes at 65°C. The emulsion was sa. cooled to 40°C, after which 1.2 mg of potassium selenium cyanate. per solvmol was added. The emulsion was then heated for 40 minutes at 65°C.

A fifth portion of the emulsion was sensitized with 2 mg potassium chloroaurate per solvmol, 0.8 mg N,N-dimethylselenurea per solvmol and 100 mg sodium thiocyanate per solvmol. The emulsion was then heated in

10 minutes at 65°C.

A sixth portion of the emulsion was sensitized with 0.8 mg N,N-dimethylselenurea per solvmol and 50 mg sodium thiocyanate per solvmol. The emulsion was then heated for 3 minutes at 65°C. It was then cooled to 4-0°C after which 2 mg of potassium chloroaurate per solv mol and 50 mg of sodium thiocyanate per solv mol were added. The emulsion was then heated for 10 minutes at 60°C.

The emulsions were then coated onto a cellulose acetate substrate with a coverage of o 58.2 mg solv per dm 2. The films were then exposed in a sensitometer with an intensity scale, developed for 5 minutes in a Kodak developer <n>DK-50", fixed, washed and dried.

The following results were obtained.

Example 15

Lack of sensitizing ability for "reducing agent" gold compound alone. Lack of sensitizing ability for non-labile selenium compound alone.

A medium grain solv bromide iodide emulsion containing 3*4% iodide was chemically sensitized with (per mole of solv halide) 4«75 mS triphenylphosphine-gold(i) chloride and 100 mg sodium thiocyanate.

Another portion of the emulsion was sensitized with 100 mg of sodium thiocyanate and 1.4 wg of potassium selenocyanate.

A third portion was sensitized with 4 rog potassium chloroaurate (equimolar amount of gold compared to sample 1) and 100 mg sodium thiocyanate.

Each of these three samples was heated for 40 minutes at 65°C.

The above-mentioned emulsion samples were then coated on a cellulose acetate substrate with a degree of coverage of 540 mg sQlv per ft.0. The films were then exposed in a sensitometer with an intensity scale, developed for 5 minutes in a Kodak developer DK-50, fixed, washed and dried.

Example 16. Activation of a non-labile selenium compound with a "reducing agent" gold compound. Simultaneous activation of the gold compound to produce a gold sensitization. The emulsion from Example 15 was chemically sensitized with (per mol solv) 4.75 mg of triphenylphosphine-gold(I) chloride, 100 mg of sodium thiocyanate and 1.4 mg of potassium selenocyanate. The emulsion was then heated for 40 minutes at 65°C.

Another portion of the emulsion was sensitized with 4 mg of potassium chloroaurate (equimolar amount of gold in relation to portion 1), 100 mg of sodium thiocyanate and 1.4 mg of potassium selenocyanate. The emulsion was heated for 40 minutes to 65°C.

A third portion of the emulsion was sensitized with 100 mg of sodium thiocyanate, 1.4 mg of potassium selenocyanate and 2.55 mg of triphenylphosphine (equimolar amount of phosphine in relation to the complex from sample 1). This emulsion was then heated for one minute at 65°C.

The emulsions were applied, exposed and processed as described in

In a comparison of portions (1) and (2) in this example, it is illustrated that the non-labile selenium compound is activated by the phosphine-gold complex (there is little or no activation in portion 2). A comparison of portion (1) and portion (3) shows that a gold sensitization also occurs in the first portion, as the non-labile selenium, which is activated with a good reducing compound in the absence of gold, only

brought a relative speed of 74.

Example 17 Inability of reducing agent-containing gold compound to chemically sensitize with labile selenium.

The emulsion from example 15 was chemically sensitized with (per solvmol) 4 mg potassium chloroaurate, 100 mg sodium thiocyanate, 1.45 mg N,N-dimethylselenorea. This portion was heated for 5 minutes at 65°C.

Another portion was sensitized with 4*75 mg of triphenylphosphine-gold(l) chloride, (equimolar amount of gold in relation to the gold-sensitizing agent in example 1), 100 mg of sodium thiocyanate and 1.45 mg of N,N-dimethyl-selenurea. This portion was heated for 20 minutes at 65°C.

The emulsions were applied, exposed and processed as described in example 15•

Example 18 The similarity between the method according to the present invention and a sensitization with gold + labile selenium.

A coarse sol bromoiodide emulsion containing 6 mol percent iodide was chemically sensitized with (per sol mol), 2 mg potassium chloroaurate, 50 mg sodium thiocyanate, 4 mg sodium thiosulfate pentahydrate, and 0.5 mg N,N-dimethylselenorea. The emulsion was heated for 5 minutes at 65°C.

Another portion was sensitized with 7*8 mg of triphenylphosphine-gold (I) chloride, 100 mg of sodium thiocyanate and 2.06 mg of complex D/~(CHo)^N/ /~C0(NCSe). The emulsion was heated for 25 minutes at 65°C.

A third portion of the emulsion was chemically sensitized with 7-8 mg of triphenylphosphine-gold(I) chloride, 100 mg of sodium thiocyanate and 1.8 mg of potassium selenocyanate. The emulsion was then heated for 20 minutes at 65°C.

The emulsion was then coated on a cellulose acetate layer with a coverage of $5.2 mg solv per dm. The films were exposed in an intensity scale sensitometer, developed for 4 minutes in a Kodak developer "D-l°/w, fixed, washed and dried.

Example 19 Illustrates the beneficial regulation that can be achieved

with respect to heating rate using gold-reducing agent complex + non-labile selenium as opposed to gold + labile selenium.

The rate curves on the attached Figure 1 show the slower heating possible with the system of gold-reducing agent + non-labile selenium.

Curves (l): Emulsion as in example 18. Chemically sensitized with (per solvmol) 6 mg potassium chloroaurate, 50 mg sodium thiocyanate + 1.89 mg N,N-dimethylselenorea. (These gold and selenium amounts are equivalent to the gold and selenium amounts in the compounds used in connection with the curves (3))•

The curves (2): The emulsion was here sensitized with 2 mg potassium chloroaurate, 50 mg sodium thiocyanate, 4 mg sodium thiosulphate pentahydrate and 0.5 mg N,N-dimethylselenorea (same sensitization as in portion 1 in example 18).

Curves (3): The emulsion was here sensitized with 7-8 mg of triphenylphosphine-gold(l) chloride, 100 mg of sodium thiocyanate + 2.06 mg of complex D<+>. (Same sensitization as for portion 2 in example 18).

It appears from the curves that:

Sensitization using equivalent gold + labile Se (curves (1)) means that the films become very unclear and never achieve a particularly high speed.

Emulsions containing optimal amounts of gold + labile selenium reach optimum within 5 minutes and could very easily be heated for too long, which would result in lower speed and high turbidity. The gold-phosphine complex with non-labile selenium reaches optimal speed after 25 minutes and with a more adjustable speed.

Example 20 Activation of inorganic isoselene cyanate complex with

a reducing agent (herein including a comparison with a labile selenium compound)

A medium-grained solv bromoiodide emulsion containing 3-4% iodide was chemically sensitized with (per solv mole) 6 mg of potassium chloroaurate, 100 mg of sodium thiocyanate + 3-3 mg of complex A (for formula see Example 22). The emulsion was then heated for 25 minutes at 65°C.

Another portion of the emulsion was sensitized in the same way as for the first portion, but by adding 20.3 mg of benzothiazole methiodide. This emulsion was heated for 25 minutes at 65°C.

A third portion of the emulsion was chemically sensitized with (per solvmol) 2 mg potassium chloroaurate, 100 mg sodium thiocyanate and 1.2 mg N,N-dimethylselenorea. The emulsion was heated for 10 minutes at 65°C.

These emulsions were then coated on a cellulose acetate substrate with a degree of coverage of o 58.2 mg solv per dm 2 . The films were then exposed in a sensitometer with an intensity scale, developed for 5 minutes in a Kodak developer "DK-50", fixed, washed and dried.

Example 21" Activation of inorganic isoselencyanate complex with a reducing agent in the absence of a gold salt. (Including a comparison with a labile selenium compound).

A first portion of the emulsion from example 20 was chemically sensitized with (per sOlvmol) 3.3 mg of complex A + 100 mg of sodium thiocyanate. The emulsion was then heated for 25 minutes at 65°C.

A second portion was sensitized in the same way as for the first portion, but by adding 20.3 mg per sSlvmol of benzothiazole methiodide. The emulsion was then heated for 10 minutes at 65°C.

A third portion was sensitized with 0.73 mg per Solvmol of N,N-dimethylalenurea and 100 mg/mol sodium thiocyanate. The emulsion was then heated for 15 minutes at 60°C.

The emulsions were then coated and treated as described in example 20.

Example 22. Activation at high gold content (nothing else

added reducing agent).

A first portion of the emulsion from Example 20 was chemically sensitized with (per mole of sulfur halide) 3.3 mg of complex B, 100 mg of sodium thiocyanate plus 6 mg of potassium chloroaurate.

Another portion was sensitized in the same way as the first, except that 18 mg of potassium chloraurate was used instead of 6 mg.

A third portion was chemically sensitized with 3.3 mg of complex C, 100 µg of sodium thiocyanate plus 6 mg of potassium chloroaurate.

A fourth portion was sensitized in the same way as the third, except that 18 g of potassium chloroaurate was used instead of 6 mg. All four portions were heated for 25 minutes at 70°C. The emulsions were then coated and treated as described in example 20.

Example 23. Activation using a high content of a precious metal sensitizer.

A portion of the emulsion from Example 20 was chemically sensitized with (per sSlvmol) 1.2 mg of potassium selencyanate plus 100 mg of sodium thiocyanate. The emulsion was then heated for 60 minutes at 70°C.

Another portion was sensitized in the same way as the first, but with the addition of 17 mg of potassium chloropalladate. The sample was heated for 60 minutes at 70°C.

A third portion was sensitized with 50 mg sodium thiocyanate +

17 mg of potassium chloropalladate, and then heated for 40 minutes at 65°C. The emulsions were strained and treated as described in example 20.

Example 24.

Three portions of the emulsion used in Example 1 were sensitized at 65°C with the compounds indicated below. The rate and turbidity of each portion were followed as a function of the sensitization time (in minutes) and the results are shown in Fig. 2.

Portion (1): (per mol sSlvhalide)

2 mg of potassium chloraurate

100 mg sodium thiocyanate

1.6 mg of N,N-dimethylselenorea

Portion (2): (per mol sSlvhalide)

4 mg potassium chloraurate

100 mg sodium thiocyanate

1.6 mg of potassium selenium cyanate

20.3 mg benzothia zolmethiodide

<*> Mole ratio noble metal to selenium compound: 5.1:1

Portion ( 3)'- (per mol solv halide)

4 mg potassium chloraurate

100 mg sodium thiocyanate

1.6 mg potassium selenium cyanate

10.15 mg benzothiazole methiodide

Comments: The amount of selenium used in the three examples is almost equivalent.

The only difference between portion (2) and portion (3) is the amount of reducing agent.

It appears from the figure that the sensitization of portion (l) reaches the maximum usable speed in the course of less than 5 minutes. F,n such a fast speed is difficult to regulate in the laboratory, and is all the more difficult in larger conditions. With the same optimal speed (and approximately the same level of turbidity), on the other hand, activating a non-labile selenium compound can be achieved, and it can be seen from the figure that a sensitization of portion (2) took 15 minutes to reach the optimum. By changing the amount of reducing agent, it is also possible to extend this time even further, and this is shown by sensitizing portion (3), where with half the amount of reducing agent in relation to portion (2), the optimal speed was reached in the run of approx. 25 minutes.

Claims (8)

1. Method for sensitizing a photographic solvent halide emulsion with a noble metal sensitizing compound and labile selenium, characterized in that the labile selenium is formed in situ by activating a non-labile selenium compound. 2. Method according to claim 1, characterized in that the non-labile selenium compound is potassium selenium cyanate or selenic acid. 3. Method according to claims 1-2, characterized in that the non-labile selenium compound is activated by means of a reducing agent. 4. Method according to claims 1-2, characterized in that the non-labile selenium compound is activated with from 2.0 to 15 mol of the noble metal sensitizing compound per mol of the non-labile selenium compound. 5. Method according to claims 1-2, characterized in that the non-labile selenium compound is activated by heating the system. 6. Method according to claim 5> characterized in that the system is first sensitized by heating in the presence of the precious metal and then sensitized. further by adding the non-labile selenium compound whereupon this is activated. 7. Method according to claim 6, characterized in that the system for activating the non-labile selenium compound is kept at a temperature varying from 55° to 70°C for a period of time varying from 20 to 100 minutes. 8. - Method according to claim 1, characterized in that the compound triphenylphosphine-gold chloride is used to activate the non-labile selenium compound and to provide a gold-sensitizing compound.