JP3136224B2 - Silver salt diffusion transfer method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a silver complex diffusion transfer reversal (DTR) method.

[0002] The principle of the DTR method is known.
SP2352014, and The Focal Press, London and New York, 1972, Andre Rott and Edith Weyde, Photographic Silver Halide Diffu
sion Processes. In the DTR method, the undeveloped silver halide of a photographic silver halide emulsion layer material that has been exposed according to information is converted into a soluble silver complex compound in a so-called "silver solvent", which is diffused into an image receiving material and Is generally reduced with a developing agent in the presence of physical development nuclei to form a silver image having an image density value that is the inverse of the silver image obtained in the exposed photographic material.

[0003] The developing agent or mixture of developing agents can be present in an alkaline processing solution or in a photographic silver halide emulsion layer material. When a developing agent or mixture of developing agents is present in the photographic silver halide emulsion material, the processing solution can be a simple aqueous alkaline solution that initiates and activates development.

The silver solvent, mostly sodium thiosulfate, is supplied from a non-photosensitive image-receiving material as described above, but is usually at least partially pre-existing in an alkaline processing solution.

[0005] The alkaline processing solution usually has a p
Alkaline substances sufficient to provide H, such as sodium hydroxide, sodium carbonate, and numerous other compounds capable of raising the pH, such as borax, sodium triphosphate, lithium hydroxide and amines, especially alkanolamines It contains.

[0006] Although the use of primary and secondary alkanolamines in alkaline solutions is sufficient to generate a pH above 10 as required, these materials require that the solution be stored and / or stored in open ambient conditions. When used, they suffer from the disadvantage that the reaction with carbon dioxide in the air results in the consumption of the alkanolamine and the required pH cannot be maintained in solution.

[0007] EP-A 398 435 proposes the replacement of primary and secondary alkanolamines with tertiary alkanolamines. It has been found that the pH can be maintained by use of this proposal, but the development rate is reduced, thereby causing a loss of overall process quality, as perceived by the user.

[0008] D, initially intended for office copying purposes
The TR method has now found wide application in the field of graphic arts, especially in the production of screen prints from continuous tone originals. For the latter, the processing characteristics remain unchanged for a large set of prints, and the gradation, optical density (transmission density for film materials, and reflection density for opaque materials such as paper materials) and screens It is particularly important that the neutrality (black) of the screen dot tones during printing satisfies a particularly high graphic arts standard compared to normal copying.

[0009] It is an object of the present invention to provide a silver complex diffusion transfer reversal method in which the storage and / or use of alkaline solutions at ambient conditions for extended periods of time can be achieved without compromising overall quality. To achieve this goal, those skilled in the art have turned their attention to the composition of the alkaline solution. Surprisingly, however, the inventors have found that this object can be achieved by modifying the composition of the silver halide emulsion.

[0010] Other objects and advantages of the present invention will become apparent from the following description.

According to the present invention, the photographic silver halide emulsion layer material, which has been exposed according to the information, is converted into a soluble silver complex compound by means of a silver solvent, which is diffused into the image-receiving material, in which an alkaline solution is present. A silver complex salt diffusion transfer reversal method for forming a silver image by reduction with a developing agent below is provided, wherein the silver halide emulsion layer contains polyoxyethylene thioether, the alkaline solution contains a tertiary alkanolamine, and It is characterized by being free from primary and secondary alkanolamines.

Thus, overall, the present invention provides two features: a silver halide emulsion containing a polyoxyethylene thioether compound; and substantially free of primary and secondary alkanolamines, and a tertiary alkanolamine. In a combination of alkaline solutions.

We have described GB1455413 which describes the use and preparation of polyoxyethylene thioethers as silver halide emulsion activators in various photographic methods.
know. However, it has not been previously proposed that the alkaline processing solution can use the activator of the silver complex salt diffusion transfer method containing a tertiary alkanolamine and that it does not contain primary and secondary alkanolamines. Still other known activators for photographic methods, such as onium-based activators, include tertiary alkanolamines and reduce the image quality and speed of DTR images obtained with alkaline processing solutions that do not contain primary or secondary alkanolamines. It was found that it was not effective for improvement.

[0014] image-receiving layer DTR-image, photographic silver halide emulsion or material can be formed on the image-receiving layer of a sheet or web material which is a separate element with respect, or also referred to as mono-sheet material or integrally DTR material Can be formed in a so-called single support material . The latter materials may be separated by an alkali-decomposable interlayer or a thin water-permeable release layer as described, for example, in U.S. Pat. No. 3,684,508, or at least one photographic silver halide emulsion layer and a water-permeable layer on top of each other. The photographic silver halide emulsion layer contains an image receiving layer having a sexual relationship,
It is optically masked from the image receiving layer with, for example, a white water permeable pigment layer as described in, for example, US Pat. Nos. 3,607,270 and 3,740,220.

The image-receiving layer contains physical development nuclei, usually in the presence of a protective hydrophilic colloid, such as gelatin and / or colloidal silica, for best imaging results.

Preferred development nuclei include sulfides of heavy metals such as antimony, bismuth, cadmium, cobalt, lead,
There are nickel, palladium, platinum, silver and zinc sulfides. Particularly suitable development nuclei are NiS · Ag ₂ S as disclosed in US-P 4,563,410. Other suitable development nuclei include salts such as, for example, selenides, polyselenides, polysulfides, mercaptans and tin (II) halides. Heavy metals or salts thereof and fogged silver halide are likewise suitable. The lead complex and zinc sulfide are both active alone and when mixed with thioacetamide, dithiobiuret and dithiooxamide. Heavy metals, preferably silver, gold, platinum, palladium and mercury, can be used in colloidal form.

The transfer behavior of the complexed silver is highly dependent on the type of binder or the mixture of binders used in the nucleation layer and the thickness of the image receiving layer. In order to obtain a sharp image having a high spectral density, the reduction of the silver salt diffused into the image receiving layer is
It must occur rapidly before lateral diffusion becomes substantial.

Image-receiving materials satisfying the above objects are described in published European patent EP 306 561 and are particularly suitable for processing with an aqueous alkaline processing liquid according to the invention.

The image-receiving layer used in the DTR method of the present invention and / or other hydrophilic colloid layers and / or other image-receiving layers.
Alternatively, the other hydrophilic colloid layer of the image receiving material may be partially cured to achieve enhanced mechanical strength. Suitable curing agents for curing the natural and / or synthetic hydrophilic colloid binder in the image receiving layer include, for example, formaldehyde, glyoxal, mokochloric acid, and chromium alum. Other suitable binders for curing the hydrophilic colloid binder in the image receiving layer include, for example, Research Di
There are vinylsulfonyl hardeners as described in sclosure 22507 (January 1983).

In the method according to the invention, the image-receiving material can be used in the form of a roll or sheet film, or in the form of a film pack, for example for in-camera processing.

Silver Halide Emulsion Material The image receiving material can be used in combination with any type of photographic silver halide emulsion material suitable for use in diffusion transfer reversal processing. The silver halide emulsion material can contain one or more hydrophilic colloid-silver halide emulsion layers.

In photographic materials to be post-exposed with a processing solution according to the present invention, whether in combination or not with a DTR image-receiving material, the hydrophilic colloidal silver halide emulsion layer is usually made of gelatin. It can be coated from any light-sensitive silver halide emulsion containing certain hydrophilic colloid binders. The weight ratio of hydrophilic colloid binder to silver halide, expressed as being equal to the amount of silver nitrate, is for example 1:
It is in the range of 1 to 10: 1.

The photosensitive silver halide used in the present invention is:
It can contain silver chloride, silver bromide, silver bromoiodide, silver chlorobromoiodide, or the like, or a mixture thereof. In order to obtain a satisfactory gradation and a sufficiently high proportion of silver halide solution required for graphic purposes, it is preferred to use a silver halide emulsion containing mainly silver chloride. For example, the commonly used silver halide is silver chloride, but a proportion of silver bromide can be present. The present inventors have found that it is particularly advantageous when the silver halide present in the silver halide emulsion contains silver chloride with at least 5 mol% of silver bromide.

The silver halide emulsions can be coarse or fine grains and can be prepared by any of the well-known methods, for example, single jet emulsions such as Lippmann emulsions, ammoniacal emulsions, thiocyanate or thioether ripened emulsions such as US- P2222264, US-P332006
9 and U.S. Pat. No. 3,271,157. Surface image emulsions may be used, or US Pat. No. 2,592,250, US Pat.
Internal image emulsions such as those described in US Pat. No. 313 and US Pat. US-P2 if desired
Mixtures of surface and internal image emulsions can be used as described in 996382.

The silver halide grains of the photographic emulsion can have a regular crystal form, such as a cubic or octahedral form, or they can have a transition form. Regular grain emulsions are described, for example, in J. Photogr. Sci. Vol. 12, No. 5 (September / October 1964), pp. 242 to 251.
The silver halide grains may have a nearly spherical shape, or they may have a lithographic shape (so-called T grains), or have a composite crystal form containing a mixture of ordered and irregular crystal forms. It may be. The silver halide grains can have a multilayer structure having a core and a shell, or the silver halide grains may contain different halide compositions and a metal dopant between.

The average grain size of the silver halide grains can be at least 0.1 μm, preferably in the range of 0.2 to 1.2 μm, and the grain size distribution can be homodisperse or heterodisperse. The homodisperse particle size distribution is 95% of the particles
Is not greater than 30% from the average particle size. However, we note that the present invention is particularly advantageous when the average (by weight) silver halide grain size is relatively large, such as greater than 0.3μ, preferably 0.5-2.0μ. Was found.

Apart from the negative working silver halide emulsion which is preferred for its high photosensitivity, a direct positive silver halide emulsion for forming a positive silver image can also be used.

With or without one or more developing agents, the silver halide emulsion may contain a pH controlling component, and other components such as stabilizers, antifoggants, development accelerators, wetting agents,
And a hardening agent for gelatin.

On the silver halide emulsion-coated side of the photographic material,
An upper layer containing a hydrophilic colloid that forms a water-permeable layer can be provided. Such an upper layer usually does not contain gelatin. Its nature is such that it does not inhibit or inhibit the spread transfer of the complexed silver and acts, for example, as an anti-stress (protective) layer. Suitable hydrophilic binders for such an upper layer include, for example, methyl cellulose, carboxymethyl cellulose sodium salt, hydroxyethyl cellulose, hydroxyethyl starch, hydroxypropyl starch,
There are sodium alginate, tragacanth gum, starch, polyvinyl alcohol, polyacrylic acid, polyacrylamide, poly-N-vinylpyrrolidone, polyoxyethylene and copoly (methyl vinyl ether / maleic acid). The thickness of this layer depends on the type of colloid used and the required mechanical strength. If present, such a layer may be at least partially transferred to the image-receiving layer without adversely affecting the imaging.

Development and diffusion transfer can be performed in different ways, for example by rubbing with a roller moistened with an alkaline processing liquid acting as a meniscus coater, by wiping with an absorbent means such as a cotton or sponge plug.
Alternatively, it can be started by immersing the material to be treated in a liquid composition. Preferably they are COPYP
The operation is carried out in an automatic operating device such as a ROOF (registered trademark of Agfa Gevaert NVV, Belgium) type CP38, CP380, CP42 and CP530 processors. DT
The R method is usually performed at a temperature in the range of 10 ° C to 35 ° C.

Hydroxyethylene thioether compound The silver halide emulsion layer contains polyoxyethylene thioether. In a preferred embodiment of the present invention, the polyoxyethylene thioether contains a repeating unit of the formula (a):

[0032]

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In the formula, R represents a substituted or unsubstituted aliphatic, aromatic or heterocyclic group. For example, R in the above formula (a) represents the following substituents: an alkyl group, an aralkyl group, a hydroxyalkyl group, an alkoxyalkyl group, an alkylthioalkyl group, an acyloxyalkyl group (the alkyl group of such a substituent is at most 5 An aliphatic, carbocyclic aromatic, or aromatic hydrocarbon bearing one or more of an acycloalkyl group such as a cyclohexyl group, an aryl group such as a phenyl group and a phenyl group substituted with alkyl, alkoxy and alkylthio. It can be a heterocyclic group.

In the present invention, a compound represented by the following formula is particularly preferred.

[0035]

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In the formula, n is 2 to 50.

Preferred polyoxyethylene thioethers have a molecular weight between 300 and 7500, most preferably 5
It has a molecular weight of 00-5000.

Such polyoxyethylene compounds are derived from polyepihalohydrins such as polyepichlorohydrin and polyepibromohydrin, which include ethers and esters, with aliphatic, carbocyclic aromatic or heterocyclic mercaptides. Can be induced by the following reaction. When using such a production method, a polyoxyalkylene compound containing a repeating unit of the following formula (c) in addition to the structural unit of the above formula (a) can be produced:

[0039]

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Wherein X is a halogen due to incomplete conversion of polyepihalohydrin. It has proved advantageous to carry out development in the presence of a polyoxyethylene compound containing units of the formulas (a) and (c) . However, there should be at least 20 mol% of randomly distributed recurring units of formula (a).

In producing the polyoxyethylene compound,
The molecular weight of the polyepihalohydrin, its ether or ester, can vary within wide limits. Dimeric compounds and generally commercially available polyepihalohydrins having a molecular weight of at most 3000 can be used. However, high molecular weight polyepihalohydrins as described in J. Polymer Sci. 40 (1959) p. 571 can also be used.

The concentration of the polyoxyethylene thioether in the silver halide emulsion layer is from 0.1 to 50 g, preferably from 1 to 10 g, per mole of silver halide present in the emulsion layer.

Alkaline treatment solution The alkaline solution is optionally combined with another alkali,
Contains more than one tertiary alkanolamine. Particularly suitable tertiary alkanolamines include, for example, (I) N-methyl-
Diethanolamine, (II) N, N-dimethyl-ethanolamine or (III) 3- (N, N-diethylamino)-
There is propane-1,2-diol. The total concentration of compounds (I), (II) and / or (III) in the alkaline solution is ideally between 0.3 mol / l and 1.5 mol / l.

The alkanolamine can reduce the pH of the processing solution without substantial increase in the absorption of small amounts of inorganic base, ie less than 0.2 mol per liter, preferably less than 0.05 mol, for example CO _2. It can be used in combination with up to 2 g / l of sodium hydroxide which brings the range from 10.5 to 13.

In order to avoid environmental concerns and to reduce the swelling of the hydrophilic colloid binder of the material to be treated, it is preferred that the treatment solution according to the invention is completely free of phosphate ions.

The optimum pH of the processing solution according to the present invention depends on the type of silver halide emulsion material to be developed, the intended development time and the processing temperature.

A silver solvent is indispensable for the DTR method. It may be supplied from a non-photosensitive image receiving material, but it is usually at least partially pre-existing in an alkaline processing solution.

The silver solvent acting as a complexing agent for silver halide is preferably a water-soluble thiosulfate or thiocyanate, such as sodium, potassium or ammonium thiosulfate or thiocyanate, or a mixture thereof. When present in an alkaline processing solution,
The molar amount of the thiosulfate compound is 0.03 to 0.1.
Preferably it is in the range of 3 mol / l.

The developing agent is preferably present in an alkaline solution, but can alternatively or additionally be present in a silver halide emulsion.

The processing solution according to the invention and the silver halide developing agent used in this method are preferably p-dihydroxybenzene compounds, for example hydroquinone, methylhydroquinone or chlorohydroquinone, and 1-phenyl-3-pyrazolidinones. It is preferred to combine with a developing agent and / or an auxiliary developing agent which is p-monomethylaminophenol. US-P33 when a very low tone for continuous tone reproduction has to be created
Preferred are developer combinations such as those described in US Pat.

Preferably, the hydroquinone developing agent is present in the processing solution according to the invention in an amount of from 0.05 to 0.25 mol per liter. The 1-phenyl-3-pyrazolidinone-based developing agent is 1.8 × 10 ^-3 per liter.
It can be present in an amount of ２．０2.0 × 10 ⁻² mol.
Particularly useful 1-phenyl-3-pyrazolidinone developing agents are 1-phenyl-4,4-dimethyl-3-pyrazolidinone, and 1-phenyl-4-monomethyl-3-pyrazolidinone. The latter type of developing agent is advantageously present in the image-receiving material.

When introduced into the photographic material, the developing agent is
It can be present in the silver halide emulsion layer or is preferably present in a hydrophilic colloid layer in water-permeable relationship therewith, such as an antihalation layer adjacent to the silver halide emulsion layer of the photosensitive material. .

The alkaline processing solution contains D in the image receiving material.
It is also preferable to include a silver image toning agent that gives a neutral (black) image tone to the silver image produced by TR.

For the DTR treatment, the aqueous alkaline treatment solution according to the invention is, for example, 30 mg to 20 mg / l.
Toning agents can be included in concentrations ranging from 0 mg. Other additives include thickeners such as hydroxyethylcellulose and carboxymethylcellulose, antifoggants such as potassium bromide, potassium iodide and benzotriazole, calcium ion sequestering agents, wetting agents such as block copolymers of ethylene oxide and propylene oxide, There are curing agents that also include sludge formation inhibitors and latent curing agents.

The present invention is further illustrated by, but not limited to, the following examples. In these examples, the following polyoxyethylene thioether was used.

[0056]

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The molecular weight is about 2832 g / mol and n is about 21.

[0058]

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The molecular weight is about 2411 g / mol and n is about 21. These compounds were made as described in GB1455413.

Example 1 Production of a negative-working silver halide emulsion photosensitive material

110 g coated on both sides with a polyethylene layer
The paper support having a weight of / m ^2, silver nitrate 1.4 g / m
One side with a toningally sensitized negative-working silver halide emulsion layer containing an amount of silver chlorobromoiodide (7.5 mol% silver bromide, 1.2 mol% silver iodide) equal to ^2. Coated. The average grain size of the emulsion is 0.15 μm with a variance of 0.46.
Had. The emulsion layer further contains hydroquinone, 1-phenyl-4-methyl-pyrazolidinone- as a developing agent.
It contained 3-one and pyrocatechol. Three additional photosensitive materials were made as described above with the addition of Compound 1 in various amounts as shown in Table 1 below.

Table 1 g of compound 1 for 100 g of AgNO ₃ material A 0 B 0.150 C 0.300 D 0.450

Preparation of the Image-Receiving Material (A ₁ ) One side of a paper support having a weight of 110 g / m ² coated on both sides with a polyethylene layer was provided with an image-receiving layer containing silver-nickel sulfide nuclei and gelatin, Coated at a dry coverage of ² g / m2. This layer has a nucleus of 1.m ² .
There and upper layer to 1 m ² in the lowermost coating of 3g of gelatin
It was then applied with a slide hopper coating to give 0.7 g of gelatin .

Exposure Method The photographic material was exposed through a sensitometric wedge in a contact exposure apparatus operated using a light source having a color temperature of 3200 ° K.

DTR Transfer Method The exposed photographic material was pre-wetted with a processing solution I described below . The contact time with the liquid was 6 seconds before pressing with the image receiving material described above. The used transfer processor is COPYP
ROOF (registered trademark of Agfa Geverdt NV)
Type CP380. Transfer contact times were 30 seconds and 45 seconds at 16 ° C and 24 ° C processing temperatures.

Evaluation All wedge prints were evaluated for the following wavelength (nm) / optical density (D) characteristics: 700 nm / D = 0; 600 nm / D = 0.2;
After a luminous filter with 00 nm / D = 1.25; 420 nm / D = 3.0, the densitometer MACBETH®
It was measured by type 1R924.

For a DTR print obtained on a paper support image receiving material, the maximum reflection density (D _R ) was measured and the gamma value (the highest gradient of the linear portion of the sensitometric curve) was determined.
Was measured. The reflection density measurement is based on the American National Standard (Sensitometry) ANSI P112.17 for photography.
(1985).

Composition of Processing Solution I

[0069] Ingredient hydroxyethylcellulose (g) 1 EDTA (g) 2 Na 2 SO 3 ( _{anhydrous) (g) 45 Na 2 S} 2 O 3 ( anhydrous) (g) 14 KBr (g ) 0.5 1- phenyl -5-mercapto-tetrazole (g) 0.08 1- (3,4-dihydroxyphenyl) -1-H-tetrazole-5-thiol (g) 0.04 DMEA (ml) 30 MDEA (ml) 35 with water It was 1 l.

EDTA = tetrasodium ethylenediaminetetraacetate DMEA = dimethylethanolamine MDEA = methyldiethanolamine

[0071] In Table 2 treatment solution I, the image-receiving element A ₁ at 16 ° C., the photosensitive material A, B, processing C and D D _R gradation materials 30 seconds 15 seconds 60 seconds 30 seconds 45 seconds 60 seconds A 0.94 1.18 1.52 0.35 0.67 1.08 B 1.11 1.74 1.60 0.87 1.28 1.49 C 1.03 1.52 1.69 0.84 1.36 1.62 D 0.92 1.59 1.72 0.97 1.43 1.67

[0072] In Table 3 treatment solution I, the image-receiving element A ₁ at 24 ° C., the photosensitive material A, B, processing C and D D _R gradation materials 30 seconds 15 seconds 60 seconds 30 seconds 45 seconds 60 seconds A 1.15 1.60 1.85 0.61 0.91 1.15 B 1.49 1.72 1.93 1.26 1.40 1.85 C 1.37 1.75 1.96 1.15 1.57 2.14 D 1.51 1.81 1.97 1.31 1.75 2.67

Tables 2 and 3 show that the coatings B to
It can be seen that D shows faster transfer characteristics than Reference Coating A.

Example 2 Production of a positive-working silver halide emulsion photosensitive material

A film support having a thickness of 100 μm was coated on one side with an anti-halation layer containing carbon black and titanium dioxide dispersed in gelatin. On the anti-halation layer, 2.65 g of silver nitrate /
A toningally sensitized positive working emulsion layer containing an amount of silver chlorobromide (9.3 mol% silver bromide) equal to m ² was coated. The average grain size of the emulsion was 0.38 μm with a dispersion of 0.20. The emulsion was ripened with a gold compound and a reducing agent and fogged. The resulting photosensitive material is designated as E. A photosensitive material (F) similar to E to which 1 g / m ² of compound 2 was added was prepared.

Preparation of Image-Receiving Material (A ₂ ) A subbed polyethylene terephthalate film support was coated with an image-receiving layer containing silver-nickel sulfide nuclei dispersed in gelatin at a dry coverage of 1.8 g / m ^2. Both sides were coated. In this layer, the core is gelatin at 1.4 g / m ^2.
4 g of zera per m ^{2 in} the bottom coating of
The chin was applied with a slide hopper coating to give it .

Exposure Method The DTR transfer method and evaluation were performed in the same manner as in Example 1 except for the following points. 1) The processing solution I was replaced with a processing solution II having the following composition. 2) The transfer contact time was 45,6 at a processing temperature of 24 ° C.
0, 75 and 90 seconds.

Composition of Processing Solution II

[0079] Ingredient hydroxyethylcellulose (g) 1.5 EDTA (g) 2.0 Na 2 SO 3 ( _{anhydrous) (g) 49 Na 2 S} 2 O 3 ( anhydrous) (g) 13 KBr (g ) 0. 5 Hydroquinone (g) 13 1-phenyl-4-methyl-pyrazolidinone-3-one (g) 4.7 1-phenyl-5-mercapto-tetrazole (g) 0.08 1- (3,4-dichlorophenyl)- 1-H-tetrazol-5-thiol (g) 0.035 DEDHPA (ml) 44.1 NaOH (50%) (ml) 7.47 The mixture was made up to 1 l with water.

DEDHPA = 3- (N, N-diethylamino) -propane-1,2-diol

Table 4 Processing solution of image-receiving material A ₂ at 24 ° C. and photosensitive materials E and F using processing solution II _DTR material 45 seconds 60 seconds 75 seconds 90 seconds E 2.0 2.7 3 3.4 3.9 F 2.6 3.4 3.8 4.4

It is clear that the photosensitive material F according to the present invention shows better transfer characteristics than the comparative photosensitive material E.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-59-143148 (JP, A) JP-A-56-165140 (JP, A) JP-A-49-90536 (JP, A) JP-A 61-143 102643 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G03C 8/06

Claims (2)

(57) [Claims] 1. The method of claim 1, wherein the photographic silver halide emulsion layer material, which has been exposed according to the information, is converted into a soluble silver complex by means of a silver solvent, and the soluble silver complex is diffused into the image-receiving material, wherein an alkaline solution is present. In a silver complex salt diffusion transfer reversal method in which a silver image is formed by reduction with a developing agent below, a silver halide emulsion layer contains polyoxyethylene thioether, an alkaline solution contains a tertiary alkanolamine, and primary and secondary A method characterized by substantially not containing a secondary alkanolamine. 2. A polyoxyethylene thioether represented by the following formula (a): 2. The method of claim 1 wherein the R comprises a substituted or unsubstituted aliphatic, aromatic or heterocyclic group.