EP0710876A1 - Black and white photographic elements - Google Patents

Abstract

A photographic element comprising a light-sensitive, Group VIII metal doped, black and white silver halide photographic emulsion layer containing less than 0.001 mol of hydrazine compound per mol of silver and comprising in said photographic layer and/or in an adjacent layer one or more compounds having a hydroxamic acid group. The presence of the hydroxamic acid compound improves contrast.

Description

This invention relates to light-sensitive black and white silver halide photographic elements and in particular to such photographic elements containing a contrast promoting compound.

One of the most important sensitometric parameters of a silver halide photographic emulsion is its contrast (gradient or gamma). Defined as the slope of the sensitometric curve between two specified densities, the contrast must be optimised for each particular imaging application. In some cases certain parts of the sensitometric curve must be modified to increase or decrease the contrast of the emulsion.

In the Graphic Arts field where half-tone dots are utilised, it is generally regarded as essential for the photographic light-sensitive medium to display a high contrast. The contrast of Graphic Arts media can be maximised in a number of ways, including the addition of metal dopants to the photographic emulsion during grain growth and the incorporation of infectious developing agents, such as hydrazine derivatives. However, both of these techniques do have limitations; addition of metal dopants is generally associated with a loss in photographic speed, whereas the use of hydrazide infectious developing agents requires a special high pH developer solution. It is also known to use a high pH, low sulphite "Lith" development process to give high contrast, but this method suffers from the disadvantages of a specialised, unstable developer and low controllability.

Thus, materials which can be added to the photographic emulsion which improve the contrast, without requiring modification of the processing conditions or having detrimental effects, are highly desirable.

Hydroxylamine is known to be a weak developing agent, as described in "The Theory of the Photographic Process", pp. 297-298, Ed. T H James, 4th edition, Macmillan Publishing Co., Inc., New York.

The use of hydroxamic acids as elements of a developer formulation has been known for many years. US 1,663,959 discloses the use of benzohydroxamic acid in a developer to reduce undesirable development effects. This patent also implies a reduction in contrast through the use of C₆H₅-C(=O)NHOH as is later explicitly mentioned in US 3,751,252 relating to photothermographic elements.

US 1,663,959 discloses a hydroxamic acid having a similar formula as that of 3,751,252 in a silver halide developer solution containing hydroquinone to reduce contrast, fogging, etc.

The use of hydroxylamine derivatives in colour developers to improve processing stability is disclosed in JP 01,124,851; EP 0,326,030; EP 0,312,984 and EP 0,279,464.

JP 03,164,735 discloses a colour photographic material incorporating compounds selected from a variety of different classes which encompass hydroxamic acid. These are claimed for improved storage stability and for reduced colour stain and colour fog.

JP 63,128,336 discloses silver halide photographic sensitive materials having improved shelf life which comprise at least one kind of the nonionic surfactant and/or at least one kind of anionic surfactant having polyoxyethylene group(s) and at least one stabilising compound represented by a general formula possessing a group selected from hydroxyalkyl, hydroxyalkoxy, hydroxyiminoalkyl, hydroxyalkyl carbamoyl, acyl, carboxyalkenyl carbohydroxamic acid, carbamoyl and hydroxy aralkyl groups.

JP 01,186,931 discloses the incorporation of hydroxamic acid derivatives into an emulsion containing a hydrazine or into adjacent layer to give a super high contrast and with high storage stability. However, this patent is restricted to only emulsions with less than 30 mol % AgBr content, and appears to refer to an infectious development process. The preferred levels of hydroxamic acid derivative are 0.0001 mol to 0.03 mol., especially preferred ranges being 0.001 to 0.03 mol, per mol of silver. It appears that the high contrast is produced by a hydrazine derivative, and hydroxamic acid is added to act as a preservative. EP 0,324,426 discloses hydrazide plus another N-OH compound to be used as a nucleation accelerator.

It has now been found that compounds containing a hydroxamic acid group may enhance the contrast of black and white photographic emulsions without the presence of a hydrazine compound.

Therefore according to the present invention there is provided a photographic element comprising a light-sensitive Group VIII metal doped, black and white silver halide photographic emulsion layer containing less than 0.001 mol of hydrazine compound per mol of silver (herein defining "substantially free of hydrazine") and comprising in said photographic layer and/or in an adjacent layer one or more compounds having a hydroxamic acid group.

The presence of the hydroxamic acid group containing compound improves contrast without requiring other modifications or causing other detrimental effects on the emulsion.

Silver halide emulsions of any composition can be considered as appropriate to this invention, such as silver chloride, silver bromide or silver iodide emulsions, as well as mixed halide compositions such as silver chlorobromide, silver iodobromide, silver iodochloride or silver chloroiodobromide emulsions. The silver halide grains may be of uniform composition or have an internal structure, such as one or more shells surrounding a core; each core or shell layer can be of any composition, as listed above. Preferred are uniform chlorobromide emulsions where the mol fraction of chloride in the grains is at least 50%.

The morphology of the silver halide grains is typically, but not limited to the cubic habit. Also useful in the invention are octahedral, tetrahedral, rhombododecahedral, icosatetrahedral, tabular or laminar grains, epitaxial growth grains, as well as mixtures of these shapes. Grains of less well defined shape may also be used.

Generally, the mean edge length of at least 50% of the grains by number is less than 2.0 microns, preferably less than 1.0 micron. Especially preferred are grains of mean edge length less than 0.4 microns down to about 0.01 micron.

The emulsion can be prepared, washed, chemically and spectrally sensitised by the techniques well known in the art.

The silver halide emulsion is doped with a group VIII metal. Group VIII metal doping refers to the process whereby during precipitation or physical ripening of the silver halide emulsion, salts of one or more Group VIII metals, e.g., trisodium hexachlororhodate (III), disodium pentachlororuthenate (III) and tripotassium hexachloroiridate (III), are present in the solution. As a result of the doping process, Group VIII metal ions of one or more types are incorporated within the interior of the silver halide grains. This is in contrast to the chemical sensitisation process, which deposits metal ions or other species on the surface of the grains. Rhodium, ruthenium, iridium and mixtures of these dopants are preferred.

The level of doping may be from 10⁻⁹ to 10⁻² moles of each Group VIII metal salt per mole of silver, preferably from 10⁻⁷ to 10⁻³ mole of each Group VIII metal salt per mole of silver.

The hydroxamic acid derivatives may be incorporated into the emulsion or a layer adjacent to the emulsion layer optionally in combination with other contrast enhancing agents. It is not envisaged that hydroxamic acid derivatives would be used in combination with contrast enhancing effective amounts of hydrazine derivatives.

The emulsion is preferably spectrally sensitised using a dye which will enhance the sensitivity of the silver halide grains at the wavelength of the exposing device. For example where a helium-neon laser is the output device, the emulsion is spectrally sensitised to 633 nm. Where an infrared laser diode is the output device, the emulsion can be sensitised, for example, in the region 650 - 830 nm. The emulsion can be suitable for continuous tone or half-tone image reproduction.

Suitable hydroxamic acid compounds for use in this invention may be represented by the general formula: X represents -C(=0)- or - SO₂-,
   R represents an organic group selected from alkyl, aryl, aralkyl, acyl, alkoxy, aryloxy or heterocyclic groups. R generally contains up to 12 skeletal atoms selected from C,N,S and O. R may also represent NR³R⁴ in which R³ and R⁴ independently represent a hydrogen atom, alkyl or aryl group.

Preferably R represents an alkyl or alkoxy group of 1 to 5 carbon atoms (e.g. methyl, ethyl, methoxy, ethoxy etc;) a phenyl group (which may be substituted, for example, with alkyl, alkoxy, OH;) NH₂ or CH₃NH.

R¹ represents an alkyl, aryl, aralkyl, acyl, or heterocyclic group which groups generally contain up to 12 skeletal atoms. Preferably R¹ represents hydrogen, alkyl of up to 5 carbon atoms, e.g. methyl, ethyl etc. or a phenyl group;

R and R¹ together may represent the necessary atoms to complete a heterocyclic ring;

R² may be hydrogen or a group that will cleave at pH > 7.0 to give hydrogen or an anion, e.g., an acyl group. Alternatively, R² may be a cation, such as, a hydrogen cation, a metal cation or an onium cation, e.g., pyridinium or ammonium.

Both carbohydroxamic acid derivatives and sulphonylhydroxamic acid derivatives may be used. Examples of compounds useful in this invention include: C₆H₅-C(=O) NHOH CH₃-C(=0)NHOH C₆H₅-CH₂OC(=O)NHOH C₆H₅-S(=O)₂NHOH NH₂-C(=O) NHOH C₆H₅-C(=O)N(CH₃)OH C₆H₅-C(=O)N(C₂H₅)OH C₆H₅-C(=O)N(C₆H₅)OH CH₃-C(=O)N(CH₃)OH CH₃-C(=O)N(C₆H₅)OH HO-C₆H₄-C(=O)N(C₂H₅)OH CH₃0-C₆H₄-C(=0)N(C₂H₅)OH CH₃-C₆H₄-C(=0)N(C₂H₅)OH C₆H₅-C(=0)N(CH₃)0(C=0)CH₃ C₆H₅-C(=0)N(C₆H₅)0(C=0)CH₃ CH₃NH-C(=0)NHOH

The compound is present in the photographic emulsion layer or in an adjacent layer in an amount from 0.1 mmol to 0.5 mol per mol silver, preferably from 1.0 mmol to 0.25 mol silver, and especially preferred from 5.0 mmol to 0.10 mol per mol silver. The hydroxamic acid derivative may be added to the photographic emulsion at any stage in its production, e.g, directly after precipitation of the grains, before or after chemical sensitisation, or as a final component just before coating. Typically the compounds are added just before coating. The hydroxamic acid derivatives can be added to the photographic emulsion in any physical form e.g. as a solid, liquid or in solution in a suitable solvent. The hydroxamic acid derivatives may be pre-dispersed into a gelatin layer before addition to the emulsion, or they may also be added as a solution in a water-immiscible solvent, so that oil droplets containing the hydroxamic acid derivative are formed in the emulsion or adjacent layer.

The hydroxamic acid derivatives are readily prepared using methods described in the literature; see, for example, "Methoden der Organische Chemie", Houben Weyl, 4th edition, Volume 8, p. 684ff.

The invention will now be described with reference to the following Examples.

Example 1

A ruthenium and iridium metal ion doped 0.32 micron cubic 64%/36% silver chlorobromide emulsion was prepared by a standard double-jet precipitation procedure. The dopant levels, expressed as moles/mole of silver were 3 x 10⁻⁷ mole Ir and 3 x 10⁻⁷ mole Ru. The emulsion was chemically sensitized with sodium thiosulphate and potassium tetrachloroaurate and spectrally sensitized to 633 nm with the benzthiazole dye:

Compounds (1) to (5) were added to samples of the emulsion in amounts as indicated in Table 1, and the emulsion was then coated on to a 175 micron clear polyester support together with a gelatin topcoat, at a silver coverage of 4.0 gm⁻².

Samples of the coatings were exposed to a Xenon flash light source which was filtered through a narrow band filter of maximum transmittance at 641 nm, and a 0 - 2.1 continuous tone wedge. The samples were processed in 3M RDC V developer at a pH of 10.6, development time of 30 seconds and development temperature of 35°C. The contrast of the samples was then determined. Con-A is measured as the slope between densities of 0.07+fog and 0.17+fog; Con-C is measured as the slope between densities of 0.50+fog and 2.50+fog.

Compound	Amount mmol/mol Ag	Con A	Con C
None	-	0.91	5.74
(1)	25	0.87	6.31
(1)	50	0.91	6.68
(2)	27	0.87	6.89
(2)	53	1.06	7.10
(3)	25	0.80	6.05
(3)	50	0.87	6.35
(4)	25	0.91	6.78
(4)	50	1.01	6.43
(5)	25	0.96	6.75
(5)	50	0.96	7.27

Example 2

The Example demonstrates that Compound (1) improves the contrast of a photographic emulsion suitable for laser argon ion exposure, when processed in Rapid Access developer.

A ruthenium and iridium metal ion doped 0.32 micron cubic 64%/36% silver chlorobromide emulsion was prepared by a standard double-jet precipitation procedure as in Example 1 with the same level of dopants. The emulsion was sensitised to 488 nm with the following dye:

The emulsion was coated on to a 100 micron clear polyester support together with a gelatin topcoat, at a silver coverage of 3.6 gm⁻² and a total gel coverage of 2.8 gm⁻². Coatings were made with the following levels of Compound (1):

Coating	Compound (1) mmol/mol Ag
2A	0.0
2B	10.0
2C	30.0
2D	50.0

Samples of the above coatings 2A-2D were exposed on an EG&G Mark VII sensitometer with a Xenon flash light source, which was filtered with a Wratten Number 4 filter, and a 0- 2.1 continuous tone wedge. Samples were processed in 3M RDC V developer at pH=10.6, with a development time of 30 seconds at 35°C. Speed points were measured at 0.2 (SP-2) and 1.0 (SP-3) density above fog. Contrast was measured between densities of 0.07 and 0.17 above DMIN (Con-A), 0.17 and 0.37 above DMIN (Con-B), and 0.50 and 2.50 above DMIN (Con-C). The following results were obtained:

Coating	Con-A	Con-B	Con-C	SP-2	SP-3	DMIN	DMAX
2A	1.22	2.52	8.56	0.40	0.23	0.03	4.86
2B	1.33	2.48	8.91	0.38	0.20	0.03	4.76
2C	1.40	2.56	9.38	0.37	0.20	0.03	4.81
2D	1.51	2.80	9.91	0.36	0.20	0.03	4.80

These results indicate a beneficial effect on Con-A, Con-B and Con-C. The samples were then subjected to accelerated ageing at 60°C and 50% RH and compared to shelf aged trials. The results are reported in the following table:

Coating	Aging/days	Con-A	Con-B	Con-C	SP-2	SP-3	DMIN	DMAX
2A	Shelf	1.20	2.49	8.75	0.41	0.22	0.03	4.33
2A	3	1.37	2.75	9.66	0.37	0.21	0.03	4.44
2A	5	1.18	2.54	9.90	0.41	0.23	0.03	4.42
2B	Shelf	1.28	2.55	8.55	0.38	0.19	0.03	4.31
2B	3	1.37	2.66	8.66	0.38	0.21	0.03	4.30
2B	5	1.32	2.50	8.84	0.41	0.23	0.03	4.31
2C	Shelf	1.30	2.65	9.40	0.38	0.21	0.03	4.33
2C	3	1.52	3.06	10.7	0.33	0.18	0.03	4.20
2C	5	1.31	2.58	9.46	0.40	0.23	0.03	4.28
2D	Shelf	1.39	2.73	9.98	0.36	0.19	0.03	4.37
2D	3	1.30	2.68	9.53	0.36	0.20	0.03	4.27
2D	5	1.28	2.68	10.5	O.37	0.21	0.03	4.33

These results do not show any significant negative effect after accelerated ageing.

Example 3

This Example demonstrates an increase in the contrast of a negative-acting Contact emulsion when Compound (1) is incorporated into the emulsion layer. Further, this Example shows that there is no detrimental effect on the DMIN level or the photographic speed.

A 0.09 micron 96%:4% AgC1Br emulsion was prepared by balanced double-jet precipitation procedure. The halide salt solution also contained rhodium (III) ions to enhance the contrast of the emulsion. The resulting emulsion which contained 2.3 x 10⁻⁴ moles Rh per mole of silver was chemically sensitized with sodium thiosulphate and potassium tetrachloroaurate.

The emulsion was then coated on to a 7 mil (0.179mm) clear polyester support material with a silver coverage of 2.5 g m⁻², and with Compound (1) incorporated as a 5% w/v methanolic solution at the levels shown below. Samples of the coatings were exposed at an appropriate level on a UV Contacting frame through a 0 - 2.1 continuous tone density wedge, and the sensitometric parameters were as described in the following Table:

Coating	Compound (1) mmol/mol Ag	Conl	DMIN	SP-1
3A	0.0	5.57	0.03	1.35
3B	3.3	6.53	0.03	1.37
3C	6.7	6.55	0.03	1.37
3D	26.7	6.81	0.03	1.38
3E	53.4	6.99	0.03	1.41
3F	106.9	6.99	0.03	1.42

SP-1 is defined as the speed at density of 0. 0 above DMIN. Conl is defined as the slope of the line connecting the points corresponding to densities of 0.10 above DMIN and 2.50 above DMIN.

Claims (11)

1. A photographic element comprising a light-sensitive, Group VIII metal doped, black and white silver halide photographic emulsion layer containing less than 0.001 mol of hydrazine compound per mol of silver and comprising in said photographic layer and/or in an adjacent layer one or more compounds having a hydroxamic acid group.
2. A photographic element as claimed in Claim 1 in which the compound(s) having a hydroxamic acid group has the general formula: in which:

   X represents -C(=0)- or -SO₂-,

   R represents an alkyl, aryl, aralkyl, acyl, alkoxy, aryloxy, heterocyclic group or NR³R⁴ in which R³ and R⁴ independently represent a hydrogen atom or an alkyl or aryl group,

   R¹ represents hydrogen an alkyl, aryl, aralkyl, acyl, alkoxy, aryloxy or heterocyclic group or

   R and R¹ together may represent the necessary atoms to complete a heterocyclic ring, and

   R² represents hydrogen or a group which will cleave at pH>7.0 to give hydrogen or an anion or R² represents a hydrogen cation, metal cation or onium cation.
3. A photographic element as claimed in Claim 2 in which:

   X is -C(=0)-,

   R² is hydrogen or -(C=0)CH₃,

   R is C₆H₅, C₆H₅CH₂, CH₃, CH₃0, NH₂, or CH₃NH, and

   R¹ is H, CH₃, C₂H₅ or C₆H₅.
4. A photographic element as claimed in any preceding claim in which said compound(s) containing a hydroxamic group is present in an amount in the range 0.1 mmol to 0.5 mol per mol of silver.
5. A photographic element as claimed in any preceding claim in which the silver halide is a uniform chlorobromide emulsion in which the mol fraction of chloride is at least 50%.
6. A photographic element as claimed in any preceding claim in which the mean edge length of the grains of silver halide is less than 0.4 microns.
7. A photographic element as claimed in any preceding Claim in which the Group VIII metal is selected from rhodium, iridium, ruthenium and mixtures thereof and the emulsion is doped with from 10⁻⁹ to 10⁻² moles of said Group VIII metal salt per mole of silver.
8. A method of preparing a photographic element comprising coating a Group VIII metal doped, black and white photographic silver halide emulsion on a support, the emulsion containing less than 0.001 mol of hydrazine compound per mol of silver characterised in that one or more compounds containing a hydroxamic acid group are incorporated into the emulsion and/or applied in a layer adjacent said emulsion layer.
9. A method as claimed in Claim 8 in which said compound is added to the photographic emulsion directly after precipitation of the silver halide grains, before or after chemical sensitisation or as a component just prior to coating, said compound being predispersed in gelatin before addition to the photographic emulsion or as a solution in water-immiscible solvent.
10. A method as claimed in Claim 8 or Claim 9 in which said compound is as defined in Claim 2 or Claim 3.
11. A method as claimed in any one of Claims 8 to 10 in which the silver halide emulsion is as defined in any one of Claims 5 to 7.