Solarization Type Silver Halide Emulsion Containing A Halogenated Hydroxyphthalein Sensitizing Dye And A Desensitizing Compound

Abstract

A direct positive silver halide photographic emulsion illustrates improved qualities when it contains at least one dye represented by the following general formula: ##SPC1## And at least one desensitizing compound represented by either of the following two general formulas: ##SPC2## X.sub.1, x.sub.2, x.sub.3, x.sub.4, or X.sub.5 can be hydrogen atom or a halogen atom, q can be 1, 2, 3 or 4, M can be a hydrogen atom, an alkali metal, NH.sub.4 or an alkaline earth metal, Y represents non-metallic atoms necessary to complete a heterocyclic ring, R can be an alkyl group or a substituted alkyl group, a, b, and r can be 1 or 2, and X represents an anion.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention:

This invention relates to a silver halide photographic emulsion, in particular to a previously fogged silver halide photographic emulsion used for direct positive materials.

2. Description of the Prior Art:

It is well known that a sensitizing dye can be added to a previously fogged silver halide photographic emulsion capable of directly giving a positive image by exposing and developing, whereby said silver halide emulsion is spectrally sensitized and, consequently, the total sensitivity is raised. It is also well known that the contrast of an image varies with the type of sensitizing dye added to the emulsion and the quantity thereof, even though the total sensitivity of the emulsion is raised.

Generally, by increasing the amount of a sensitizing dye which is added to a direct positive silver halide photographic emulsion, the total sensitivity thereof is markedly raised, but, in many cases, a satisfactory image is not obtained, mainly due to lowering of the maximum density (D.sub.max) and contrast.

We have made various studies on such problems and have found that a halogen-substituted hydroxyphthalein dye represented by the following general Formula (I) is excellent as a dye capable of raising the total sensitivity while keeping a predetermined maximum density and contrast:

GENERAL FORMULA (I) ##SPC3##

in which X.sub.1, X.sub.2, X.sub.3, X.sub.4 and X.sub.5 represent, respectively, hydrogen atoms or halogen atoms, q represents 1, 2, 3 or 4 and M represents a hydrogen atom, an alkali metal such as Na or K, NH.sub.4 or an alkaline earth metal such as 1/2 Ca.

When a sensitizing dye is added to a direct positive silver halide photographic emulsion, furthermore, the total sensitivity thereof is raised. However, in some cases, "re-reversal" is enlarged, hardly resulting in a satisfactory white color.

The term "re-reversal" describes the phenomenon that, as shown by the dotted curve of the characteristic curve in FIG. 1, if a direct positive photographic emulsion showing solarization is given a sufficient amount of exposure, the density eventually ceases and then shows a new upward trend (see C. E. Kenneth Mees; "The Theory of the Photographic Process," Revised Edition, pages 243 and 244, 1942).

This "re-reversal", dependent upon the process of preparting the silver halide photographic emulsion, is particularly large when the emulsion is sensitized with the halogen-substituted hydroxyphthalein dye represented by the foregoing general Formula (I). Accordingly, it is hard to use this dye in a practical process.

It is the principal object of the invention to provide a direct positive silver halide photographic emulsion having high sensitivity, which has a low minimum density without "re-reversal" while holding a predetermined maximum density and a high contrast.

SUMMARY OF THE INVENTION

The present invention provides additives to a direct positive silver halide photographic emulsion which provide high sensitivity, low minimum density and a lack of "re-reversal" while providing a predetermined maximum density and high contrast.

The additives comprise at least one dye represented by the following general Formula (I): ##SPC4## in which X.sub.1, X.sub.2, X.sub.3, X.sub.4 and X.sub.5 represent, respectively, a member selected from the group consisting of hydrogen atoms or halogen atoms, q represents 1, 2, 3 or 4, and M represents a member selected from the group consisting of a hydrogen atom, an alkali metal, NH.sub.4 or an alkaline earth metal; and at least one desensitizing compound represented by the following general Formula (II):

in which Y represents non-metallic atoms necessary for completing a heterocycylic ring, R represents an alkyl group or a substituted alkyl group, a, b, and r represent 1 or 2, and X represent an anion; or at least one desensitizing compound represented by general Formula (III):

in which Y, r and b have the same meaning as in general Formula (II).

The present invention thus provides a direct positive silver halide photographic emulsion with high sensitivity, low minimum density, no re-reversal and a predetermined maximum density and high contrast.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 are plots of density versus light sensitivity (log E).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The heretofore mentioned object can be accomplished by incorporating a desensitizing compound represented by the following general Formula (II) or general Formula (III) in a direct positive silver halide photographic emulsion, sensitized with the halogen-substituted hydroxyphthalein dye represented by the foregoing general Formula (I):

GENERAL FORMULA (II)

in which Y represents non-metallic atoms necessary for completing a heterocyclic ring such as thiazolines, thiazoles, benzothiazoles, naphthothiazoles, oxazoles, benzoxazoles, naphthoxazoles, benzoselenazoles, naphthoselenazoles, benzimidazoles, 2-quinolines, 4-quinolines and indolenines, R represents an alkyl group one to four carbon atoms such as a methyl or ethyl group, or a substituted alkyl group one to four carbon atoms such as 2-hydroxyethyl, 2-methoxyethyl, carboxymethyl 2-carboxyethyl, 2-sulfoethyl, 3-sulfo-propyl or carboethoxymethyl group, X represents an anion such as a halide, toluenesulfonate or a perchlorate ion and a, b and r represent 1 or 2; and

GENERAL FORMULA (III)

in which Y, r and b have the same meaning as in General Formula (II). Examples of the compound represented by General Formula (I) are as follows: ##SPC5##

The dyes represented by the foregoing general Formula(I) are well known and sold.

Examples of the compound represented by General Formula (II) and (III) are as follows: ##SPC6##

The desensitizing compounds represented by the foregoing general Formulas (II) and (III) are well-known, and are capable of lowering the minimum density (D.sub.min) of a direct positive silver halide photographic emulsion, as disclosed in U.S. Pat. No. 2,541,472.

It is surprising that the dye of general Formula (I), according to the invention, has an excellent action for sensitizing a direct positive halide photographic emulsion, since it has either no sensitizing effect on an ordinary negative emulsion or a much lower sensitizing effect than a cyanine sensitizing dye or merocyanine sensitizing dye.

The direct positive silver halide photographic emulsion, sensitized with the dye represented by the general Formula (I) has such features that the sensitivity is high, the maximum density (D.sub.max) is not substantially lowered and the contrast is not lowered. However, its "re-reversal" and minimum density (D.sub.min) are so high that it cannot be put to practical use.

Further, when the desensitizing compound represented by the general Formula (II) or (III) is added to an ordinary negative photographic emulsion sensitized by a spectral sensitizing dye, the spectral sensitizing action of the dye fades away, and the whole sensitivity thereof lowers.

It has now been found that the foregoing disadvantage of a direct positive silver halide photographic emulsion sensitized with the dye represented by the general Formula (I) can be overcome by the coexistence of the desensitizing compound represented by the general Formula (II) or (III) in said emulsion. Ordinarily, the dye represented by the general Formula (I) and the desensitizing compound represented by the general Formula (II) or (III) are added to an emulsion, preferably in the form of a solution. As suitable solvents, there can be used water, methyl alcohol and ethyl alcohol.

The amount of the dye represented by general Formula (I) which is added to a silver halide photographic emulsion for direct positives is effectively 10-150 mg., particularly 20-100 mg per kg of the emulsion, while the amount of the desensitizing compound represented by the general Formula (II) or (III) which is added is effectively 10-150 mg, particularly 20-100 mg per kg of the emulsion, the proportion by weight of the dye compound (I) and desensitizing compound (II) or (III) being preferably 1:10 to 10:1.

Illustrative of the silver halides of the invention are silver chloride, silver bromide, silver chlorobromide, silver chloroiodide, silver iodobromide and silver chloroiodobromide.

The silver halide photographic emulsion for direct positives used in the invention is fogged to a maximum density by light or by the addition of a chemical fogging agent. Such a chemical fogging agent must fog silver halide without affecting the emulsion. Thiourea dioxide, stannous chloride, formaldehyde or hydrazine are usually used as a chemical fogging agent.

After the fogging operation, a solution of the dye represented by the general Formula (I) and a solution of the desensitizing compound represented by general Formula (II) or (III) are added to the emulsion (with adequate agitation), and the emulsion is then coated onto a support member. The dye represented by the general Formula (I) and the desensitizing compound represented by the general Formula (II) or (III) may be added to the emulsion in any optional sequence, or along with ordinary additives such as coating aids and hardening agents. Suitable supports are, for example, a glass sheet, cellulose derivative film, synthetic resin film or baryta paper.

The following examples are given in order to illustrate the invention in detail without limiting the same.

EXAMPLE 1

A silver chloroiodide (iodide 1.3 mol percent, chloride 98.7 mol percent) emulsion was fogged with hydrazine dihydrochloride and, its pH and pAg were respectively adjusted to 5.6 and 6.7. To the emulsion were added, while stirring adequately, the dye represented by the general Formula (I) and then the desensitizing compound represented by the general Formula (II). The emulsion was then coated onto a cellulose triacetate base. For comparison, only the dye of general Formula (I) was added to the emulsion and coated onto a base. After drying, the resulting photographic materials were exposed by means of a sensitometer through a step wedge.

The thus exposed materials were developed with a developing solution having the following composition.

Formula of developer Metol 4 g. Hydroquinone 10 g. Anhydrous sodium sulfite 60 g. Anhydrous sodium carbonate 2.5 g. Water to 1,000 ml.

A direct positive image, after being developed, was fixed with a fixing solution containing sodium thiosulfate, washed with water and dried. Measurement of the optical density was carried out by the use of a densitometer. The results are tabulated below. --------------------------------------------------------------------------- TABLE 1

Compound Compound of of general general White formula I formula II Sensi- Test (mg/kg (mg/kg tivity Max. Min. No. emuls.) emuls.) (log E) density density ---------------------------------------------------------------------------

1 1.80 2.3 0.07 2 I-10(62.5mg) 0.38 2.3 0.15 3 I-10( ") II-6(59.0mg) 0.66 2.2 0.08 4 I-10( ") II-6(118mg) 1.03 2.2 0.07 5 I-6(55.5mg) 0.82 2.3 0.34 6 I-6( ") II-6(59.0mg) 1.23 2.3 0.15 7 I-6( ") II-6(118mg) 1.43 2.3 0.10 8 I-12(73.5mg) 0.87 2.3 0.11 9 I-12( ") II-6(59.0mg) 1.39 2.3 0.07 10 I-12( ") II-6(118mg) 1.44 2.3 0.07 __________________________________________________________________________

The "re-reversal" effect is shown in FIG. 2 in which the numerals 2, 3 and 4 correspond to Test Numbers in Table 1. It is evident therefrom that the "re-reversal" is lowered by adding the desensitizing compound represented by general Formula (II) or (III).

EXAMPLE 2

A silver chloroiodobromide (bromide 2.4 mol percent, iodide 1.3 mol percent, chloride 96.3 mole percent) emulsion was fogged with hydrazine dihydrochloride, and its pH and pAg were adjusted to 5.6 and 6.7, respectively. To the emulsion were added the dye represented by the general Formula (I), while stirring adequately, and then the desensitizing compound represented by the general Formula (II) or (III), while stirring adequately. The emulsion was then applied to a cellulose triacetate base. For comparison, only the dye represented by general Formula (I) was added to the foregoing fogged emulsion and coated onto a base. After drying, the resulting photographic materials were exposed and developed in the same manner to Example 1, thereby obtaining the results shown in Table 2. --------------------------------------------------------------------------- TABLE 2

Compound Compound of of general general White formula I formula II Sensi- Test (mg/kg (mg/kg tivity Max. Min. No. emuls.) emuls.) (log E) density density ---------------------------------------------------------------------------

1 1.67 2.2 0.06 2 I-10(125mg) 0.08 2.1 0.14 3 I-10( ") II-3(55 mg). 0.38 2.0 0.08 4 I-10( ") II-3(110mg) 0.77 2.0 0.07 5 I-6(110mg) 0.73 2.1 0.32 6 I-6( ") II-4(55mg) 1.14 2.1 0.15 7 I-6( ") II-4(110mg) 1.34 2.0 0.11 8 I-12(37mg) 0.65 2.2 0.09 9 I-12( ") II-5(54mg) 1.20 2.1 0.07 10 I-12( ") II-5(108mg) 1.25 2.1 0.07 __________________________________________________________________________

Claims

We claim:

1. A direct positive silver halide photographic emulsion which has been previously fogged to maximum density containing at least one dye represented by the following general Formula (I): ##SPC7##

in which X.sub.1, X.sub.2, X.sub.3, X.sub.4 and X.sub.5 represent, respectively, a member selected from the group consisting of hydrogen atoms or halogen atoms, q represents 1, 2, 3 or 4, and M represents a member selected from the group consisting of a hydrogen atom, an alkali metal, NH.sub.4 or an alkaline earth metal; and at least one desensitizing compound represented by the following general Formula (II):

in which Y represents non-metallic atoms necessary for completing a heterocyclic ring, R represents an alkyl group or a substituted alkyl group, a, b, and r represent 1 or 2, and X represents an anion; or at least one desensitizing compound represented by general Formula (III):

in which Y, r and b have the same meaning as in general Formula (II).

2. The direct positive silver halide photographic emulsion claimed in claim 1, wherein the halogen atoms in X.sub.1, X.sub.2, X.sub.3, X.sub.4 and X.sub.5 of the general Formula (I) are selected from the group consisting of chlorine, bromine and iodine.

3. The direct positive silver halide photographic emulsion claimed in claim 1, wherein said heterocyclic rings containing Y in general Formula II are selected from the group consisting of thiazolines, thiazoles, benzothiazoles, naphthothiazoles, oxazoles, benzoxazoles, naphthoxazoles, benzoselenazoles, naphthoselenazoles, benzimidazoles, 2-quinolines, 4-quinolines and indolenines.

4. The direct positive silver halide photographic emulsion claimed in claim 1, wherein said alkyl group in R of the general Formula II is a methyl or ethyl group.

5. The direct positive silver halide photographic emulsion claimed in claim 1, wherein said substituted alkyl group in R of the general Formula II is selected from the group consisting of 2-hydroxyethyl, 2-methoxyethyl, carboxymethyl, 2-carboxyethyl, 2-sulfoethy, 3-sulfopropyl or carboethoxymethyl group.

6. The direct positive silver halide photographic emulsion claimed in claim 1, wherein the proportion, by weight, of said dye represented by general formula I to said desensitizing compound represented by general Formula II or III is from 1:10 to 10:1.

7. The process which comprises coating am emulsion as recited in claim 1 onto a support and thereafter imagewise exposing said emulsion; and developing said exposed emulsion to form a silver image in the unexposed areas of the emulsion.

8. The direct positive silver halide photographic emulsion of claim 1, wherein said dye represented by general Formula I is present in an amount of from 10 to 150 mg/Kg of emulsion.

9. The direct positive silver halide photographic emulsion of claim 1, wherein said dye represented by general Formula I is present in an amount of from 20 to 100 mg/Kg of emulsion.

10. The direct positive silver halide photographic emulsion of claim 1, wherein said dye represented by general Formula I is a member selected from the group consisting of ##SPC8##

11. The direct positive silver halide photographic emulsion of claim 1, wherein said desensitizing compound represented by general Formula II is a member selected from the group consisting of ##SPC9##

12. The direct positive silver halide photographic emulsion of claim 1, wherein said desensitizing compound represented by general Formula III is a member selected from the group consisting of ##SPC10##

13. The process of claim 7, wherein said dye is present in an amount of from 10 to 150 mg/Kg of emulsion.

14. The process of claim 7, wherein said dye is present in an amount of from 20 to 100 mg/Kg of emulsion.

15. The process of claim 7, wherein the proportion, by weight, of said dye to said compounds is within the range of from 1:10 to 10:1.

16. A direct positive silver halide photographic emulsion when has been previously fogged to maximum density containing

a. at least one dye selected from the group consisting of ##SPC11##

b. at least one desensitizing compound selected from the group consisting of ##SPC12##

or

c. at least one desensitizing compound selected from the group consisting of ##SPC13##

said dye being present in an amount of from 20 to 100 mg/Kg of emulsion,

and

the proportion, by weight, of said dye to said desensitizing compound ranging from 1:10 to 10:1.