Silver halide photographic light-sensitive material

Abstract

 A silver halide photographic light-sensible material comprised of twin crystals having an aspect ratio of not less than 3, prepared in a protective colloid, containing hydrogen peroxide is disclosed. If the material is spectrally sensitized before the chemical sensitization, a material having a high sensitivity and a high image quality improved in sharpness and graininess is obtainable.

Description

FIELD OF THE INVENTION

[0001] The present invention relates to a silver halide photographic light-sensitive material having a high quality image improved in sharpness and graininess. More particularly, the present invention relates to a silver halide photographic light-sensitive material for medical application, which is free from image deteriorations such as pressure desensitization and roller marks caused by mechanical pressure and has a high diagnostic property.

BACKGROUND OF THE INVENTION

[0002] In recent years, high sensitivity and high image quality are increasingly demanded of light-sensitive materials in concert with the progress of rapid processing. In silver halide photographic light-sensitive materials for medical application, for example, there are demanded light-sensitive materials which provide high quality images having a high detecting capability at a small X-ray dosage.

[0003] In general, the sensitivity and sharpness of silver halide photographic light-sensitive materials are primarily controlled by silver halide grains themselves. Accordingly, many improvements have so far been proposed on silver halide grains. For example, there are disclosed tabular silver halide grains, in which the sensitivity/size ratio is raised for each grain in order to obtain a higher sensitivity and a higher image quality, in Japanese Pat. O.P.I. Pub. Nos. 111935/1983, 111936/1983, 111937/1983, 113927/1983 and 99433/1984. Since these tabular silver halide grains have a large surface area per volume, they can adsorb much spectral sensitizing dyes on the grain surface to provide a high sensitivity.

[0004] Further, as a technique to improve sensitivity and graininess, Japanese Pat. O.P.I. Pub. No. 92942/1988 proposes use of tabular silver halide grains in which silver iodide rich cores are provided and Japanese Pat. O.P.I. Pub. No. 163451/1988 proposes use of a silver halide emulsion comprised of tabular grains having twin planes.

[0005] However, all of these techniques have limits in reconciling sensitivity and image quality, and further improvements in quality have been strongly demanded.

SUMMARY OF THE INVENTION

[0006] Accordingly, a first object of the invention is to provide a silver halide photographic light-sensitive material having a high sensitivity and a high image quality improved in sharpness and graininess. A second object of the invention is to provide a silver halide photographic light-sensitive material free from undesirable desinsitization and fog caused by roller pressure or other external pressure in handling.

[0007] That is, the objects of the invention are achieved by a silver halide photographic light-sensitive material having, at least on one side of a support, at least one silver halide emulsion layer, wherein said silver halide emulsion layer is comprised of tarbular silver halide twin crystal grains having an aspect ratio of not less than 3 prepared in a protective colloid containing a hydrogen-peroxide-treated gelatin, and said grains are spectrally sensitized before chemical sensitization with the addition of sensitizing dyes. The invention will hereinafter be described in detail.

DETAILED DESCRIPTION OF THE INVENTION

[0008] In a photographic emulsion, characteristics of gelatin used are very important as shown by its physical controlling capabilities, which have not only a large effect on chemical sensitization but also influence on formation and growth of silver halide crystal grains. And such gelatin's characteristics are known to undergo a large change according to extraction conditions or other manufacturing conditions. One of the important characteristics is permeability, and it is preferable for a photographic gelatin to have a permeability of not less than 92%, especially not less than 94%.

[0009] As a means to raise the permeability, ther are known a method to filter gelatin to remove impurities or a method to bleach gelatin with hydrogen peroxide.

[0010] Bleaching of gelatin with hydrogen peroxide to oxidize impurities and certain amino acids contained therein is a general method to prepare an inert gelatin.

[0011] In the invention, it is found that an emulsion prepared by use of gelatin of high permeability treated with hydrogen peroxide enhances the effect of the invention much more.

[0012] The addition amount of hydrogen peroxide to enhance the permeability is 0.1 to 50 g, preferably 0.1 to 30 g, and especially 0.1 to 10 g per kilogram of gelatin. The pH at which gelatin is treated with hydrogen peroxide is preferably higher than 5.6, especially 6.0 to 12.

[0013] The temperature of this treatment is preferably 35 to 70°C, especially 40 to 65°C. This hydrogen peroxide treatment may be carried out at any stage between extration and gelation in the manufacturing process of gelatin.

[0014] Next, there will be described a preferable preparation procedure of an emulsion according to the invention which uses the above hydrgen-peroxide-treated gelatin. A silver halide emulsion used in the invention is preferably prepared by depositing silver halide on monodispersed seed crystal grains. The particularly preferred manner is to provide a growing process to grow monodispersed spherical twin seed crystal grains described in Japanese Pat. O.P.I. Pub. No. 6643/1986.

[0015] That is, the following three stages are provided sequentially as the preparation process of the silver halide photographic emulsion of the invention:

(a) Nucleus grain formation process to form crystal nuclei of the above silver halide grains,

(b) Seed grain formation process to form silver halide seed grains from the above nucleus grains, and

(c) Growing process to grow the seed grains.

[0016] The nucleus grain formation process in the invention is defined as the process before the seed grain formation process, which may cover not only a period from start of adding a water-soluble silver salt to a protective colloid solution to a time at which formation of new crystal nuclei substantially ceases, but a period to grow grains after that.

[0017] The growth condition of the above growing process may be any of the acid process, neutral process and ammoniacal process, and there may be used conventional methods described, for example, in Japanese Pat. O.P.I. Pub. Nos. 6643/1986, 14630/1986, 112142/1986, 157024/1987, 18556/1987, 92942/1988, 151618/1988, 1613451/1988, 220238/1988 and 311244/1988.

[0018] By-products, excessive salts or other unnecessary components may be removed by usual flocculation methods or noodle washing methods.

[0019] The average silver iodide content of the silver halide used in the invention is 0.1 to 45 mole%, preferably 0.5 to 25 mole% and especially 1 to 20 mole%.

[0020] Silver halide grains according to the invention are spectrally sensitized in a process before chemical sensitization with the addition of spectral sensitizing dyes. "A process before chemical sensitization" mentioned here may be a physical ripening process to prepare silver halide grains or a desalting process to remove excessive salts, or a period from completion of the desalting to start of addition of chemical sensitizing dyes in chemical sensitization. Of them, the physical ripening process is preferred, and the time when the physical ripening is completed is particularly preferred. Spectral sensitizing dyes used in the invention are not particularly limited in kinds and may be any of conventional spectral sensitizing dyes.

[0021] "Twin crystals" according to the invention are silver halide crystal grains having one or more twin planes in one cystal grain. Classification of twin forms is discussed in detail by E. Klein and E. Moiser in Photographishe Korrespondenz Vol. 99, p. 99 and Vol. 100, p. 57.

[0022] The term "silver halide grains comprised of twin crystals" used in the invention means that at least 70% of the total projection area of the silver halide grains is comprised of grains having twin planes. This ratio is desirably not less than 75%, more desirably, at least 80% of the grains are ones having twin planes.

[0023] The twin crystals according to the invention [are] may be any of ones having (111) face, ones having (100) face and a mixture thereof, but ones having (111) face are preferred.

[0024] Further, the twin crystals according to the invention are preferably tabular crystal grains having two primary parallel planes facing with each other.

[0025] The diameter/thickness ratio, namely aspect ratio, of these tabular silver halide grains is 3 to 20, preferably 3 to 15 and especially 4 to 13 on the average. This average value may be obtained by taking an average of cross sections of all the tabular grains, or may be determined as a ratio of the average diameter of the total grains to the average thickness of the total grains.

[0026] The diameter of a tabular silver halide grain is given as a diameter of a circle having a projected area equal to the primary plane area of the grain.

[0027] This diameter is generally 0.1 to 5.0 µm, preferably 0.2 to 4.0 µm and especially 0.3 to 3.0 µm.

[0028] The silver halide emulsion used in the invention is preferably one of which grain size distribution is monodispersed. The silver halide composition of an emulsion used in the silver halide photographic light-sensitive material of the invention may be any of silver iodobromide, silver iodochloride and silver iodochlorobromide, but silver iodobromide is preferred for its capability of providing a high sensitivity.

[0029] A silver halide emulsion used in the invention is comprised of tabular crystal grains having an aspect ratio of not less than 3.

[0030] Such tabular crystal grains allow an emulsion to have a high spectral sensitization efficiency and a capability of providing images of improved graininess and sharpness as disclosed, for example, in British Pat. No. 2,112,157, U.S. Pat. Nos. 4,439,520, 4,433,048, 4,414,310, 4,434,226 and Japanese Pat. O.P.I. Pub. Nos. 113927/1983, 127921/1983, 138342/1988, 284272/1988, 305343/1988. Preparation of an emulsion comprised of tabular crystal grains can be made by methods disclosed therein.

[0031] The above emulsions may be a surface latent image type which forms a latent image inside of a grain or an internal latent image type which forms a latent image inside of a grain, or a type which forms a latent image on the surface and inside of a grain. These emulsions may use, in the stages of physical ripening or grain preparation, a cadmium salt, lead salt, zinc salt, thallium salt, iridium salt or its complex salt, rhodium salt or its complex salt, or iron salt or its complex salt. The emulsion may be subjected to a desalting treatment by means of noodle washing or flocculation. Preferable desalting methods include, for example, a method to use a sulfo-group-containing aromatic hydrocarbon type aldehyde resin described in Japanese Pat. Exam. Pub. No. 16086/1960 and a method to employ exemplified high-molecular weight flocculants G 3 or G 8 in Japanese Pat. O.P.I. Pub. No. 158644/1988.

[0032] The emulsion according to the invention may use various photographic additives in processes before and after physical ripening or chemical ripening. Conventional additives are those described, for example, in Research Diclosure Nos. 17643 (December, 1978), 18716 (November, 1979) and 308119 (December, 1989). Compound types and locations of descriptions of the additives shown in these three numbers of Research Disclosure are as follows:

Additives	RD-17643		RD-18716	RD-308119
	Page	Class	Page Class	Page	Class
Chemical sensitizers	23	III	648 upper right	996	III
Sensitizing dyes	23	IV	648-649	996-8	IV
Desensitizing dyes	23	IV		998	B
Dyes	25-26	VIII	649-650	1003	VIII
Developing accelerators	29	XXI	648 upper right
Antifoggants & stabilizers	24	IV	649 upper right	1006-7	VI
Brightening agents	24	V		998	V
Hardeners	26	V	651 left	1004-5	X
Surfactants	26-27	XI	650 right	1005-6	XI
Antistatic agents	27	XII	650 right	1006-7	XIII
Plasticizers	27	XII	650 right	1006	XII
Lubricants	27	XII
Matting agents	28	XVI	650 right	1008-9	XVI
Binders	26	XXII		1009-4	XXII
Supports	28	XVII		1009	XVII

[0033] Supports usable in the light-sensitive material of the invention are, for example, those described on page 28 of the above RD-17643 and on page 100, of RD-308119.

[0034] Preferable supports are plastic films; the surface of such supports may be coated with a subbing layer or subjected to corona discharge or X-ray irradiation to enhance adesion to a coating layer.

EXAMPLES

[0035] The present invention is described hereunder with the examples, but the embodiment of the invention is not limited to them.

[0036] A lime-treated ossein gelatin was extracted at 45°C and divided into two equal parts; one part was labeled as ossein gelatin A, and the other part was treated with hydrogen peroxide and labeled as ossein gelatin B.

Preparation of comparative emulsion E-1

(Preparation of seed emulsion S-1)

[0037] 

A₁:

40 g of ossein gelatin A, 23.7 g of potassium bromide and 10 ml of surfactant* were dissolved in water to give a total volume of 4000 ml.

B₁:

600 g of silver nitrate was dissolved in water to give a total volume of 803 ml.

C₁:

16.1 g of ossein gelatin and 420 g of potassium bromide were dissolved in water to give a total volume of 803 ml.

D₁:

235 ml of aqueous ammonia (28%)

[0038] The apparatus described in Japanese Pat. O.P.I. Pub. No. 160128/1987 was used after fixing on it six each of feed nozzles for solutions B₁ and C₁ toward the lower part of the stirring blades. While stirring solution A₁ at 430 rpm and an average temperature of 40°C, solutions B₁ and C₁ were added thereto by the double-jet method at a flow rate of 62.8 ml/min. The flow rate was kept at this level for 4 minutes and 46 seconds and then gradually raised so as to reach a final flow rate of 105 ml/min in a total addition time of 10 minutes and 45 seconds, during which the pBr was maintaind at 1.3 with potassium bromide. The temperature of the reaction liquor and stirring rate were made to an average temperature of 20°C and 460 rpm, respectively, in 30 minutes after completion of the addition.

[0039] Then, solution D₁ was added within one minut thereto, followed by a 5-minute Ostwald ripening. During the ripening, the potassium concentration was kept at 0.028 mole/l, the ammonia concentration at 0.63 mole/l, and the pH at 11.7.

[0040] Upon termination of the 5-minute ripening period, the liquor was neutralized to pH 5.7 with acetic acid to stop the ripening and then subjected to desalting and washing in usual manners. Electron microscopic observations of seed emulsion S-1 obtained as above proved that the emulsion was comprised of spherical grains having an average grain size of 0.20 µm and a variation coefficient of grain size distribution of 34%.

[0041] Silver halide emulsion E-1 comprised of tabular twin crystals was prepared by use of seed emulsion S-1 and the solutions shown below.

A₂:

16 g of ossein gelatin A, 3 ml of surfactant* and 0.27 molar equivalent of seed emulsion S-1 were dissolved in water to give a total volume of 1000 ml.

B₂:

5 g of ossein gelatin A, 307 g of potassium bromide and 8 g of potassium iodide were dissolved in water to give a total volume of 880 ml.

C₂:

448 g of silver nitrate was dissolved in water to give a total volume of 880 ml.

D₂:

2.7 g of ossein gelatin A and 19 g of potassium bromide were dissolved in water to give a total volume of 500 ml.

E₂:

27 g of silver nitrate was dissolved in water to give a total volume of 530 ml.

* Surfactant (10% methanol solution)
(CH₂CH₂CH₂O)p[(CH₂CH₂O)mCOCH₂CH₂COONa]₂   p=17, m=2.7

[0042] Solutions B₂ and C₂ were added by the double-jet method in 38 minutes to solution A₂ being stirred vigorously. The addition rate of solutions B₂ and C₂ was linerly increased so as to make the final addition rate 2.4 times the initial addition rate. Then, solutions D₂ and E₂ were added thereto in 6 minutes at a constant rate.

[0043] During the addition, the pAg was kept at 10. After completion of the addition, the pH was adjusted to 6.0 and then 400 mg per mole silver of spectral sensitizing dye (A) described later was added, followed by stirring for 30 minutes. Subsequently, excessive salts in the liquor were removed by desalting using an aqueous solution of Demol made by Kao Atlas and an aqueous solution of magnesium sulfate. E-1 obtained had a pH of 5.90 and a pAg of 8.5 at 40°C. Electron microscopic observations of the emulsion proved that it was comprised of grains having an average grain size of 0.90 µm, an average thickness of 0.41 µm and a variation coefficient of grain size distribution of 28%, and that the percentage of tabular grains having an aspect ratio of 2 or more was 80% and the average aspect ratio of grains having an aspect ratio of 2 or more was 2.2.

Preparation of emulsion E-2 of the invention

[0044] Seed emulsion S-2 was prepared in the same manner as with seed emulsion S-1 used in comparative emulsion E-1, except that hydrogen-peroxide-treated ossein gelatin B was used. During the ripening, the potassium bromide concentration was kept at 0.026 mole/l, the ammonia concentration at 0.63 mole/l, and the pH at 11.6. This seed emulsion S-2 was found to be comprised of spherical grains having an average grain size of 0.20 µm and a variation coefficient of grain size distribution of 18% by electron microscopic observations.

[0045] Subsequently, silver halide emulsion E-2 comprised of tabular twin crystal grains was prepared by use of seed emulsion S-2 in a similar manner as with comparative emulsion E-1. The pAg and pH of this emulsion after desalting were 8.5 and 5.90, respectively, at 40°C. Electron microscopic observations of the emulsion proved that it was comprised of tabular grains having an average grain size of 1.20 µm, an average thickness of 0.24 µm and a variation coefficient of grain size distribution of 19%, and that the percentage of tabular grains having an aspect ratio of 2 or more was 85% and the average aspect ratio of grains having an aspect ratio of 2 or more was 5.0.

Preparation of emulsion E-3 of the invention

[0046] Seed emulsion S-3 was prepared in the same manner as with seed emulsion S-2 used in emulsion E-2, except that the temparature of Ostwald ripening was kept at 15°C on the average. During the ripening, the potassium bromide concentration was kept at 0.026 mole/l, the ammonia concentration at 0.63 mole/l, and the pH at 11.7. Electron microscopic observations of this seed emulsion proved that it was comprised of spherical grains having an average grain size of 0.18 µm and a variation coefficient of grain size distribution of 20%
   Using seed emulsion S-3, silver halide emulsion E-3 comprised of tabular twin crystal grains was prepared in a similar manner as with comparative emulsion E-1. After desalting, this emulsion showed a pH of 5.91 and a pAg of 8.5 at 40°C. According to electron microscopic observations, the emulsion was comprised of tabular grains having an average grain size of 2.13 µm, an average thickness of 0.22 µm and a variation coefficient of grain size distribution of 21%; the percentage of tabular grains having an aspect ratio of 2 or more was 90%, and the average aspect ratio of tabular grains having an aspect ratio of 2 or more was 9.7.

Preparation of comparative emulsion E-4

[0047] Silver halide emulsion E-4 comprised of tabular twin crystal grains was prepared in the same manner as with comparative emulsion E-1, except that the spectral sensitizing dye was not added before the desalting of seed emulsion S-3.

[0048] After desalting, the emulsion prepared showed a pAg of 8.5 and pH of 5.90 at 40°C. Electron microscopic obsevations of this emulsion proved that it was comprised of tabular grains having an average grain size of 2.13 µm, an average thickness of 0.22 µm and a variation coefficient of grain size distribution of 21%, and that the percentage of tabular grains having an aspect ratio of 2 or more was 90% and the average aspect ratio of tabular grains having an aspect ratio of 2 or more was 9.7.

Preparation of emulsion E-5 of the invention

[0049] Silver halide emulsion E-5 comprised of tabular twin crystal grains was prepared in the same manner as with comparative emulsion E-1, except that hydrogen-peroxide-treated ossein gelatin B was used in preparation of seed emulsion S-3. After desalting, the emulsion obtained had a pAg of 8.5 and a pH of 5.91 at 40°C. Electron microscopic obsevations of this emulsion proved that it was comprised of tabular grains having an average grain size of 2.35 µm, an average thickness of 0.21 µm and a variation coefficient of grain size distribution of 20%, and that the percentage of tabular grains having an aspect ratio of 2 or more was 90% and the average aspect ratio of tabular grains having an aspect ratio of 2 or more was 11.2.

[0050] To each of the emulsions were added spectral sensitizing dyes (A) and (B) at a weight ratio of 200:1 in a total amount of 800 mg per mole of silver halide, and each emulsion was chemically ripened by adding 2.4 X 10⁻³ mole per silver halide of ammonium thiocyanate and optimum amounts of chloroauric acid and hypo, and then stabilized by adding 2 X 10⁻² mole of 4-hydroxy-6-methyl-1,3,3a,7-tetrazaindene.

[0051] Subsequently, the emulsion additives described later and lime-treated gelatin were added to each emulsion to obtain a coating solution.

Spectral sensitizing dye (A)

[0052]    Anhydrous sodium 5,5'-dichloro-9-ethyl-3,3'-di-(3-sulfopropyl)oxacarbocyanate

Spectral sensitizing dye (B)

[0053]    Anhydrous sodium 5,5'-di-(butoxycarbonyl)-1,1'-diethyl-3,3'-di-(4-sulfobutyl)benzimidazolocarbocyanate
   Further, a coating solution for protective layer was prepared as described later.

[0054] The coating solutions prepared were double-layerdly and simultaneously coated in the order of silver halide emulsion layer and protective layer, with a slide hopper type coater, on both sides of a polyethylene terephthalate film base provided with 175 µm thick subbing layers. The thickness of the emulsion layer was adjusted to give a silver amount of 1.6 g/m² and a gelatin amount of 1.8 g/m² for each side; the thickness of the protective layer was adjusted to give a gelatin amount of 1.1 g/m² for each side. The additives incorporated in the emulsion are shown below; addition amounts thereof are per mole of silver halide.

[0055] The additives used in the protective layer are shown below; addition amounts thereof are per liter of the coating solution.

[0056] The sample prepared was sandwiched between fluorescence intensifying screens KO-250 made by Konica Corp. and exposed through an aluminium step wedge at a tube voltage of 90 KV, a tube current of 20 mA and an illumination time of 50 msec. Subsequently, it was developed for 30 seconds at 35°C with a developer XD-90 and fixed with XF in an automatic processor model KX-500 (each of which is made by Konica Corp.), and then washed and dried according to usual manners. For the processed sample, a reciprocal of the exposure amount necessary to obtain a density of base density + fog density + 1.0 was determined. The sensitivities shown in Table 1 are sensitivities relative to that of sample No. 1 which is set at 100.

Evaluation of sharpness

[0057] Evaluation of sharpness (MTF) was made by use of a FUNK test chart SMS5853 (product of Konica Medical) on a sample treated with the same lamp voltage, intensifying screens and processing conditions as in the above sensitometry. The exposure amount was adjusted for each sample so as to make the average of various desities made by the FUNK test chart 1.30 ± 0.02. The larger the value is, the better the sharpness is.

Evaluation of pressure desensitization

[0058] After conditioning for 2 hours at 23°C and 36.5% RH, each sample was bent up to about 280° with a radius of curvature of about 2 cm in the same environmental conditions. Three minutes later, X-rays were irradiated to the sample for 0.06 sec at a tube voltage of 80 KV and a tube current of 100 mA through an aluminium wedge. The irradiated sample was processed in the same manner as in the above sensitometry and then visually checked for pressure desensitization.

Evaluation of graininess

[0059] Using the sample prepared to evaluate the pressure desensitization, the graininess was visually evaluated.

[0060] The visual evaluations of the pressure desensitization and graininess were made using a five-grade rating, in which 5 means the best and 1 the poorest.

[0061] The results obtained are shown in Table 1.

Table 1

Sample No.	Emulsion		Sensitivity	Dmax	MTF	Graininess	Pressure desensitization	Remarks
	Kind	Seed emulsion
1	E-1	(S-1)	100	3.14	0.50	1	2	Comparison
2	E-2	(S-2)	152	3.15	0.62	4	5	Invention
3	E-3	(S-3)	230	2.88	0.66	4	5	Invention
4	E-4	(S-3)	187	2.89	0.53	3	1	Comparison
5	E-5	(S-3)	275	2.66	0.68	5	4	Invention

[0062] As apparent from Table 1, the silver halide photographic light-sensitive materials according to the invention are high in sensitivity, excellent in sharpness and graininess and moreover improved in pressure desensitization.

EFFECT OF THE INVENTION

[0063] According to the present invention, a silver halide photographic light-sensitive material with high sensitivity and high sharpness was obtained without lowering graininess of images. In addition, pressure desensitization was also improved with the present invention.

Claims

1. A silver halide photographic material comprising: a support being provided thereon, at least one layer containing silver halide grains comprised of twin crystals in tabular form, having an aspect ratio of not less than 3, prepared in a protective colloid, containing a hydrogen peroxide treated gelatin; and
the silver halide grains being spectrally sensitized in a process before chemical sensitization, by spectral sensitizing dyes.

2. The silver halide photogrphic material of claim 1, wherein the aspect ratio is 3 to 20.

3. The silver halide photographic material of claim 2, wherein the aspect ratio is 4 to 13.

4. The material of claim 1, 2 or 3, wherein the silver halide grains contain 0.1 to 45 mole % of silver iodide.

5. The material of claim 4, wherein the silver halide grain contain 1 to 20 mole % of silver iodide.

6. The material of claims 1, or 2 to 5, wherein an average diameter of the silver halide grains is 0.2 to 4.0 µm.

7. The material of claim 6, wherein the average diameter of the silver halide grains is 0.3 to 3.0 µm.

8. The material of claims 1 or 2 to 7, wherein the hydrogen peroxide treated gelatin is prepared by adding 0.1g to 50g of hydrogen peroxide per 1kg of gelatin.

9. The material of claim 8, wherein the hydrogen peroxide is 0.1g to 10g per 1 kg of gelatin.

10. The material of claim 8 or 9, wherein the hydrogen peroxide treated gelatin is prepared at pH 6.0 to 12.0, a temperture at 40°C to 65°C.

Amended claims

Amended claims in accordance with Rule 86(2) EPC.

11. A method of preparing a silver halide emulsion containing twin crystal tabular silver halide grains having an average aspect ratio of at least 3, comprising steps of:
   forming said silver halide grains in the protective colloid containing a gelatin treated by hydrogen peroxide,
   spectrally sensitizing said grains by using a sensitizing dye,
   chemically sensitizing said grains after said spectral sensitization.

12. The method of claim 11, wherein the aspect ratio is 3 to 20.

13. The method of claim 12, wherein the aspect ratio is 4 to 13.

14. The method of claim 11, wherein the silver halide grains contain 0.1 to 45 mole % of silver iodide.

15. The method of claim 14, wherein the silver halide grains contain 1 to 20 mole % of silver iodide.

16. The method of claim 15, wherein an average diameter of the halide grains is 0.2 to 4.0 µm.

17. The method of claim 16, wherein the average diameter of the silver halide grains is 0.3 to 3.0 µm.

18. The method of claim 11, wherein the hydrogen peroxide added to 1 kg of the gelatin is 0.1g to 50g.

19. The method of claim 18, wherein the hydrogen peroxide added to 1kg of the gelatin is 0.1g to 10g.

20. The method of claim 19, wherein the gelatin is treated by the hydrogen peroxide at pH 6.0 to 12.0.

21. The method of claim 20, wherein the gelatin is treated by the hydrogen peroxide at 40°C to 65°C.

22. The method of claim 11, wherein a permeability of the gelatin is not less than 92 %.

23. The method of claim 22, wherein the permeability of the gelatin is not less than 94 %.