US3251692A - Stabilized physical developments - Google Patents

Description

United States Patent 3,251,692 STABILIZED PHYSICAL DEVELOPMENTS Hendrik Jonker and Comelis Johannes Dippel, both of Emmasingel, Eindhoven, Netherlands, assignors to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware No Drawing. Application Oct. 2, 1964, Ser. No. 405,644, which is a division of application Ser. No. 845,098, Oct. 8, 1959, now Patent No. 3,157,502. Divided and this application Apr. 5, 1965, Ser. No. 445,760

. 2 Claims. (CI. 96-66) This invention relates to developers used in the purely physical developments of photographic images and to processes employing such developers.

This application is a division of our copending application Serial No. 405,644, filed October 2, 1964, which is in turn a division of our application Serial'No. 845,098, filed October 8, 1959, now US. Patent No. 3,157,502.

In the usual type of development employed in photography, the so-called chemical development, the metal in the visual photographic image is obtained by the reduction of metal ions of the water insoluble metal compound present in the latent image in the exposed light sensitive layer.

The developing solution employed in chemical develop- .ment initially does not contain any dissolved compounds of the visual image metal. However, after the chemical developer is used for a while it may contain in solution ions of the visual image metal.

In the purely physical development the intensification or development of the latent image is carried out by treating the latent image with a developing solution which contains a water soluble reducible metal compound and a photographic reducing agent.

In physical developing practically all of the metal in the resultant visual image is formed by the selective reduction of metal ions or complex metals anions supplied by said water soluble metal compound.

The term photographic reducing agent is to be understood hereinto mean a compound which, in the dissolved state, is capable of reducing the said metal ions or complex metal anions into free metal and the activity of which in the physical developer under the conditions otherwise prevailing therein is accelerated by the presence of a photographic latent image so as to obtain a sufficiently selective deposition of metal on this latent image.

The photographic reducers which may be used in physical development are frequently similar to those which are also used in chemical development.

They often satisfy the formula wherein C represents a carbon atom, a and b each represent hydroxyl (OH) groups, amino groups or substituted amino groups (NH NHR, NRR' wherein R and R are alkyl or aryl radicals groups), n is zero or an integer.

It is possible to distinguish three large classes of photographic reducing agents which correspond to the above general formula.

(1) That of the hydroquinone type: a andb both are OH groups. This class includes, in addition to hydroquinone itself, inter alia: pyrocatechol, pyrogallol, gallic acid and ascorbic acid.

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(2) That of the aminophenol type: a is an OH-group and b is an amino group which is substituted or not substituted. This class includes inter alia: oand p-aminophenol, p-methylaminophenol-sulphate (metol), p-hydroxyphenylglycine (Kodurol).

(3) That of the phenylenediam-ine type: a is an amino group or a mono-substituted amino group, b is an amino group which is substituted or non-substituted. This class includes inter alia: oand p-phenylenediamine and N,N- diethyl-p-phenylenediamine.

In addition, there are some further photographic reducing agents which do not satisfy the above-mentioned formula, such as l-phenyl-3-pyrazolidone (Phenidone) and several inorganic photographic reducing agents, such as ferrous, titanous and vanadous ions, which are commonly used in the form of complex compounds, for example the ferrous-oxalate complex.

In purely physical developers, only metal ions and complex metal anions of metals which are more precious than copper i.e. mercury, silver, platinum, gold or palladium may be used in combination with photographic reducing agents. These metals in the instant application will be hereinafter designated as precious metals. A physical developer frequently used is, for example, a solution of silver nitrate in Water to which hydroquinone and p-phenylenediamine have been added. In addition, some further sub stances are usually added to such a developer, which substances serve to increase the length of life or to control the velocity of development. These are, for example, organic acids, buffer mixtures or substances which enter into reaction with the precious metal salt to form thereby complex metal anions.

The purely physical development hitherto employed has disadvantages which has prevented its general introduction into the photographic techniques. These disadvantages are due to the fact that physical developers, in contradist-inction to chemical developers, are unstable systems due to a homogeneous reaction being liable to occur in the solution between the precious metal compound and the reducing agent in addition to the heterogeneous reaction on the latent image, whereby the latter is intensified, which homogeneous reaction then results in the spontaneous formationof metal germs in the solution and in the photographic material outside of the latent image which germs form precipitates. In addition, a spontaneous catalyzed reduction may occur on the wall of the developing vessel and this reduction likewise gives rise to unwanted loss of a metal. Once such metal germs having spontaneously been formed, their growth will compete with the deposition of the metal on the latent image obtained by the reaction of light. This spontaneous formation of the metal precipitates, of course, also takes place when the physical developer is not in use and this results in fairly rapid deterioration of such developers While depositing metal and in considerable contamination of the vessel employed. Such developers are thus uneconomical in use.

The spontaneous formation of the metal germs and resultant formation of precipitates in the photographic material outside the latent image obtained by illumination may give rise to unwanted fogging of the ultimate photographic image. The spontaneous dissociation reaction in physical developers is usually accomplished in a period of time which is not very much longer than the time required for the development of the metal latentimage into a photographic visual metal image of desired optical density.

It is known that, in certain cases, it is possible to increase the length of life of a purely physical developer, for example, by reducing the temperature, by dilution, by decreasing the pH or by the addition of the oxidation product of the reducing agent. However, these steps cause a corresponding increase in the time of development, thus rendering such processes serviceable for the technique only in certain cases or in combination with additional steps. Such a step is, for example, to increase the temperature of photographic material containing an amount of such a developer sufiicient for building up the image. Developers thus treated have sometimes been referred to as stabilized developers. However, they are not stabilized in the sense of the present invention in which the spontaneous separation of the precious metal from the developer is likewise materially decreased, but without at the same time considerably retarding the velocity of development. The first-mentioned kind of increase of the length of life will be referred to hereinafter as inactivation and the relevant developers will be referred to as inactivated developers. If, on the other hand, as is frequently desirable, efforts are made to shorten the time of development in the purely physical development, for example by increasing the temperature, by the use of higher concentrations of the reacting constituents, or by increasing the pH, this is always at the expense of the length of life of the developer, while the possibility of fogging considerably increases, in certain cases even to an extent such that the selectivity of the precipitation of metal on the photographic metal latent graphic process based on the photo-sensitivity of silver halide, the chemical development has been preferred. However, there are cases that chemical development is impossible and hence physical development is the only possibility of intensifying the photographic latent images, since the image-producing metal, in contradistinction to the chemical development, is not yet present as a nonsoluble compound in the area of the image. However, also in these cases in which chemical development is possible, physical development is sometimes desirable in view of the better quality of the image, for example, in con nection with the high resolving power that can be obtained with it.

It is therefore a principal object of this invention to provide purely physical developers which are stable, that is, in which there is little or no precipitation of metal from the precious metal compound in the developer outside of the latent photographic image.

Another object of this invention is to provide purely physical developers which do not cause fogging.

These and other objects of the invention will be apparent from the description that follows.

According to this invention it has been found that the precipitation of the precious metal from the developer outside of the latent image because of the homogeneous reaction between the photographic reducing agent and the precious metal compound of the developer can be eliminated to a very large extent by the addition of one or more suitable ionic surface active agents or surfactants to the developer. As a result of the addition of these surfactants the life of the developer is increased at least 50% and in one case is 10,000 times that of the corresponding unstabilized developer.

The use of these ionic surfactants is based on the different behaviours of the ionic surfactants in physical development, so far as the metal precipitates spontaneously formed in the developer and the visual metal image in the photographic material are concerned. Such a selectivity is, of course, essential to proper action of the dethe metal precipitates spontaneously formed, without.

nevertheless affecting the growth of the photographic metal visual image in the exposed layer in a manner which is of practical importance.

The process of the invention may be carried out with all those photographic materialsin which a physically developable metal latent image may be obtained directly or indirectly by the action of light. These photographic materials include first of all those materials which contain a photosensitive compound, the light reaction product of which as such already behaves as a physically developable photographic metal latent image, for example materials containing silver halide as the photosensitive compound. In addition, they include all those photo graphic materials which contain a photosensitive com- 7 pound'the light reaction product of which as such is not physically developable, but by a secondary reaction may be converted or react into a physically developable photographic metal latent image. If the light reaction product is a metal compound, this secondary reaction consists in isolating metal particles from the metal compound, as is the case, for example, in the photographic process in which use is made of the-photosensitivity of the so-called Eder solution and in which the light reaction product is mercurous chloride. Numerous photosensitive compounds are also known, the light reaction product of which in a secondary reaction may react in the presence of moisture with mercurous-ions or with silver-ions while forming physically developable latent mercury images and latent silver images respectively. Such photosensitive compounds, such as aromatic diazonium compounds, diazosulphonates and diazocyanides and inorganic complex compounds, are used in a large number of processes for the manufacture of photographic images.

Surfactants or surface-active substances, that is to say, substances which are adsorbed at the boundary surface of two phases, are usually organic compounds having amphi-. pathic properties. Their molecule or ion contains one or more hydrophobic and one or more lipophilic groups, which are bonded together either directly or via, for ex ample, an ester, ether or amide bond. The hydrophobic groups are, for example, aliphatic carbon chains having from 8 to 18 carbon atoms with a very small afiinity to the medium (water), in contradistinction to the hydrophilic groups which have a great affinity to water. The latter are therefore sometimes referred to as solubilising or polar groups. These may be, for example, sulphonate or pyridinium groups.

The surfactants may chemically be divided into two classes:

(a) The ionic surfactants, the hydrophilic group of which carries the charge and which thus occur in the form of an anion, a cation or a zwitterion. Reference is then made to anion-active, cation-active and amphoteric surfactants, respectively.

(b) Thenon-ionic surfactants, the hydrophilic group of which is non-ionisable.

During the establishment of the present invention, it has been found that a favourable technical effect in the sense previously described can be obtained only when use is made of surfactants of the first-mentioned category that is the ionic surfactants. The non-ionic surfactants are thus unserviceable as development stabilizers. The serviceable surfactants chiefly belong to the classes of the cation-active, anion-active and amphoteric micellproducing surfactants and to the class of the cation-active macro-molecular surfactants.

In chemical developers, too, surfactants are sometimes used, for example of the quaternary ammonium type compounds. These may considerably speed up the develbathed for a short time, for example, in a 0.2% solution of lauryl-pyridinium-p-toluenesulphonate. The problem of which the present invention provides a solution in the physical development does not exist, however, in the chemical development and the effect of the surfactants is therefore of quite a different nature.

As previously mentioned, physical developers may have greatly differing compositions; they may react in an acid, neutral or alkaline reaction and they may contain different compounds of precious metals, photographic reducing agents of different kinds and many sorts of auxiliary materials. Consequently, it will be evident that the choice of the ionic surfactants used for obtaining stabilization of development cannot be arbitrary. For example, those few ionic surfactants which produce in one way or another a precipitation with one of the constituents of the physical developer cannot be used. Also there may be insuflicient activity by the surfactant because of the low dissociation of the surfactant at the pH of the developer concerned.

In order to determine whether a given ionic surfactant is serviceable as a physical developer stabilizer under the conditions which prevail in the physical developer chosen, the following test may be carried out.

By means of a sensitometer wedge, identical photographic metal latent images are manufactured on two foils of one of the photographic materials defined above. In covered developing vessels one of these foils is developed in a developer containing the surfactant to be tested (A), the other foil being developed in the corresponding developer from which this surfactant is omitted (-B). The two foils are developed as long as is necessary for obtaining a predominantly neutral-gray copy of the wedge in developer B. In the event of the length of life of developer B being so short as to be incapable of developing into one neutral-grey copy, the development is stopped when the activity of the developer has ceased; After the development of the first two foils has been terminated, new latent image foils identical with the first-mentioned are introduced some more times into the two developers at given intervals, the period of which may naturally be varied as a function of the length of life of the developers. The lengths of life of the two developers are thus approximately determined, that is to say, the times which elapse between the moment when the two developers were prepared and the moments when their developing power has disappeared almost completely. This test has at the most a semi-quantitative character, since the spontaneous formation of the metal precipitate in non-stabilized developers is naturally not reproducible with great accuracy. In order to avoid wrong conclusions which might result from the said fluctuations, one sets as a criterion of activity that the length of life of developer A with respect to that of developer B must be increased at least by 50%.

During this test it is necessary to ensure that the total amount of image metal which is consumed for building up the image in all the copies of the wedge developed in one and the same developing bath, is not more than of the initial potential supply of metal of this bath.

It is not possible generally to indicate the limits of the effective range of concentration of the surfactants. Most of the surfactants commercially sold are technical products which usually consist of a mixture of homologues which possess the same hydrophilic group and hence are not clearly defined chemically. Otherwise these technical products are, on the whole, quite serviceable without further purification, insofar as they do not show unwanted reactions in the physical developer such as formation of a deposit. However, during the establishment of the invention, it has been found that the number of carbon atoms of the lyophilic group influences the lower limit of activity when starting from pure, well defined compounds. Thus, for example, for a given physical developers it was found that for octylamine acetate this limit exists at a concentration of about 0.1 mol, for decylamine acetate at a concentration of 0.03 molar and with dodecylamine acetate at a concentration of 0.003 molar.

These results indicate that the stabilization effect of the surfactants may be related to micelle format-ion by the hydrophilic ions of the surfactants at or about the small precious spontaneous metal germs from the precious metal compound thus preventing the germs from growing large enough to precipitate out of the developer solution.

With increasing concentration of the surfactant, the

stabilizing effect in certain cases increases, then reaches a maximum and finally disappears completely. The latter is frequently accompanied by flocculation of the surfactant, in which event the activity frequently returns to an increased extent, if the fiocculated surfactant is solubilised with another ionic surfactant of the same charge or with a non-ionic surfactant. In other cases, however, a decline in activity upon increasing concentration of the surfactant could not be determined. It is not yet quite clear how all these phenomena must be interpreted. With reference to the sensitometer wedge test described supra, it is possible in all cases to determine the most active concentration or concentrations of the surfactant empirically.

During the experiments carried out in formulating this invention it was found by micro-electrophoretic measurements on the physical developers that the surfactants acted upon the electrophoretic charge of the precious metal germs. In the absence of the surfactants it was found that these precious metal germs had a charge depending to a large extent on the other ingredients in the developer.

,Thus it was found that the electrophoretic charge of the spontaneous silver germs was distinctly negative in a metol-citric acid-silver nitrate developer and distinctly positive in a corresponding p-phenylene diamine-citric acid-silver nitrate developer. In corresponding alkaline developers in which sodium sulphite was employed in addition the charge on silver germ in both cases was found to be negative. The spontaneously formed germs of mercury were however, found to be positive in a hydroquinone, nitric acid, mercurous nitrate developer.

The surfactants act to increase the existing charge of the precious metal germs or to provide a new strong charge of opposite polarity on the precious metal germ depending on whether cation or anion-active surfactants are employed and whether the charge on the precious metal germ is the same or opposite to that of the hydrophilic ion released by the surfactant. By thus effecting the electrophoretic behaviour of the spontaneously formed precious metal germs in the physical developers the growth of these germs into sizes large enough to precipitate out of the solution is prevented.

The action of the hydrophilic ions on the charge of spontaneous precious metal germs involves probably the formation of micelles which as stated before prevents the growth of these germs. A strong positive charge of the germs will prevent the approach of positive metal ions, whereas a strong negative charge may prevent transmission of electrons to the germs and approach of negative complex metal ions. Consequently, in certain cases, a hydrophilic ion of one type of charge and, in other cases, one of the other type of charge, but frequently hydrophilic ions of both types of charge result in a stabilizing effect in a physical developer. However, the photographic test above described always gives an answer to the question whether a given stabilizer is effective in certain kind of developer.

Nevertheless, it remains a surprising fact that the photographic metal latent image is not acted upon in the same manner as are the grems spontaneously formed, in other words, that any appreciable decrease in the velocity of development does not occur. Evidently, the position is such that formation of micelles does not occur in the latent image and that micelles formed outside latent image cannot enter it.

It has been found that most effective stabilization of the physical developer is ensured,'at least if the surfactant chosen does not become inactive due to reaction with one of the constituents of the developer, for example due to formation of a precipitate, if the surfactant is chosen to be such that the charge of the surface-active ion is opposite to the electrophoretic charge of the precious metal germs formed spontaneously in the corresponding physical developer from which the surfactant has been omitted and if the concentration of the surfactant is sufiicient so as to be capable of giving the spontaneous metal germs the charge of surface-active ion.

A very good stabilizing effect may be obtained in physical development by means of acid reacting developers containing soluble silver compounds or mercury compounds if the reducing agent employed is a compound of the hydroquinone type and the stabilizer is an alkylaryl sulphonate derived from diphenyl.

Finally, physical gold developers may best be stabilized by means of the same alkylaryl sulphonates which are derivatives of diphenyl.

8 EXAMPLES The specified formulas are included in the accompanying table.

I. A superficially saponified film of cellulose acetate was sensitized by impregnating for 2 minutes with an aqueous solution containing 0.15 gram mole of the sodium salt of o-methoxy-benzenediazosulphonic acid and As previously mentioned, a given surfactant may sometimes show a considerably smaller stabilizing effect than could be expected due to its being flocculated under the conditions which prevail in the physical developer or due to its having itself unduly low solubility. In this case, the activity of the surfactant may be considerably increased by solubilization. This maybe effected by means of another ionic surfactant of the same charge type or by means of a non-ionic surfactant.

A process is also known for obtaining metallic images in photographic material by purely physical development of photographic metal latent images, the photographic material being developed in the form of a stack of sheets in a physical developer which may, be inactivated, if desired, and which contains an amount of metal salt not more than about three times as much as suflices for building up the visual images. According to the in- .vention, by the use of surfactants in the developers, much more beautiful results, less fogging and less contamination of the sheets due to finely-divided metal lossely deposited on them is obtained.

In combination with known steps by which the purely physical development is used in a continuous process, the invention imparts to the developer properties rendering it even much attractive for practical use.

It is possible to carry out a developing process in which the developing liquid is continuously supplied from two separate supply solutions which are stable in themselves. The invention may then successfully be used by adding a development stabilizer to at least one solution, so that better results are obtained and the process is accomplished more economically.

If a certain amount of photographic materials is physically developed several times in succession in a given amount of developer which is stabilized and possibly inactivated, the present invention also permits of regenerating this developing liquid at will by adding metal salt or an aqueous solution thereof which may be provided with a stabilizer. Thev process of regenerating the developer may, of course, also be carried out continuously.

In addition, the known continuous process in which the photographic material is caused to absorb an amount of inactivated developer at least sufiicient for building up the images and in which the development is accomplished substantially outside this supply, may be considerably improved by the use of the invention, since by means of stabilizers it is possible to prepare developer solutions which are durable for a much longer time than are the corresponding non-stabilized solutions and which nevertheless exhibit a reasonable developing activity.

The invention will now be explained in detail with reference to a number of examples.

0.1 gram mole of cadmium acetate per liter, followed by wiping off and drying. A piece of this film was exposed to the light of a mercury lamp behind a sensitometer wedge and subsequently treated with an aqueous solution containing 0.005 gram mole of mercuous nitrate and 0.01 molof nitric acid per liter, resulting in a mercury germ image being formed (the so-called germ image foil). After the formation of the germ image, the foil was rinsed in distilled water. Astrip of the germ image foil was physically developed for 10 minutes in a fresh solution of 0.5 g. of metal, 2 g. of citric acid and 0.2 g. of silver nitrate in g. of distilled water. The silver germs spontaneously formed in this solution were found to have a negative electrophoretic charge.

Another strip of the same germ image foil was developed for the same period in a fresh solution which, in addition to the said constituents, also contained 0.02 g. of the cation-active surfactant Sapamine KW." This is the methyl sulphate of monostearylamido-ethylene-trimethyl-amine (Formula I). It was determined by electrophoretic means that. the germs formed spontaneously in the solution had a very distinct positive charge. With certain intervals, which in this case were about 30 minutes, new strips of germ image foils identical with the first-mentioned were introduced into the two-developing solutions and developed therein for 10 minutes.

This procedure was continued until the developing power of each solution had disappeared almost completely, while taking care that in total not more than about 10% of the silver potentially present in each of the developers at the beginning of the test was used for building up the image. The stabilized developing solution became inactive in a period of time which was three times as long (the stabilization factor) as that in which the developer without the stabilizer became inactive. A delay in the development was not established at all in this and the following examples of stabilized physical developers, unless special statements are made to the contrary.

Instead of using the above-mentioned photosensitive material, it is alternatively possible in this and the corresponding subsequent examples to utilize similar materials obtained by impregnation of regenerated cellulose film or superficially saponified cellulose-ester film with solutions of other aromatic diazosulphonates such, for example, as the sodium salt of p-methoxyor p-ethoxybenzene diazosulphonic acid, the sodium salt of chloro- 2-methyl-4 benzenediazosulphonic acid-1, and the sodium dimethoxy-3,4 salt of benzenediazosulphonic acid-1, or

with solutions of other photosensitive compounds from cal' development took place for 8 minutes in solutions containing per 100 g. of distilled water:

(a) 0.33 g. of potassium gold chloride 1.3 g. of oxalic acid (b) as a and, in addition, 0.2

g. of Aresklene-400 (Formula II) The length of life of developer b was at least twice as long as that of developer a.

Table Formula Trade Name Source 1 [C 1sHa7fi-NCzH4N (CHa)s] (504C113) Sapamiue KW Ciba.

(C4Ho): II CsHrCe 0H Aresklene 400 Monsanto Chem. Co. (SOaNB)! III (CsH;NH-C QH;:)X (X=Cl or Br) Flxanol C Lilgllfg and 00. Imperial Chem.

' v NCH,

IV CH3(CH,),,-C

N CH;

For Amine 0, n=l6 M01. weight=355 Amine O Amine s, 11:16 Mol. welght=360 Amine s )Almse Chem- R is a substituent having a comparatively low molecular weight.

NCHg.NHO3 V 0 1E530 Amine 220 nitrate Uralon Carbide and Carbon orp. NCH1 CHg-CHgOH VI CUHEafi-NCjHAN(C:H5)z-CHZC 0 0H Sapamine A Clba.

/0Hr-CH7CHI-N(CH1CH1OH)1 VII--. C1sHa1N Ethoduomeen T/m Armour and Co.

CHr-CH OH vnr.--- c.r1.-(:.H.{ S6553 }Aresket s00 Monsanto Chem. 00.

IX CH (CH;)1.C=(f(CH:)1CH1SO;Na Lissapol O Imp. Chem. Ind.

or CH:(CH2)1CH CH-(CH:)7-*CH OH S0,Na

While we have described our invention in connection with specific embodiments and applications, other modifications thereof will be readily apparent to those skilled in this art without departing from the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

1. A stabilized photographic physical developer comprising an aqueous solution of a water soluble gold salt reducible to metallic gold, a photographic reducing agent for reducing said gold salt to gold and as an anionic surfactant an alkylaryl sulfonate containing a diphenyl moiety, said surfactant being present in an amount sufficient to increase the life of the developer at least 50% when compared to the life of an identical developer without said surfactant.

References Cited by the Examiner UNITED STATES PATENTS 3,157,502 Il /1964 Ionker et a1. 96-49 NORMAN G. TORCHIN, Primary Examiner.

Claims (1)

1. 2. A STABILIZED PHOTOGRAPHIC PHYSICAL DEVELOPER COMPRISING AN AQUEOUS SOLUTION OF A WATER SOLUBLE GOLD SALT REDUCIBLE TO METALLIC GOLD, A PHOTOGRAPHIC REDUCING AGENT FOR REDUCIN SAID GOLD SALT TO GOLD AND AS AN ANIONIC SURFACTANT A DIBUTYL-O-PHENYLPHENOL SODIUM DISULPHONATE, SAID SURFACTANT BEING PRESENT IN AN AMOUNT SUFFICIENT TO INCREASE THE LIFE OF THE DEVELOPER AT LEAST 50% WHEN COMPARED TO THE LIFE OF AN IDENTICAL DEVELOPER WITHOUT SAID SURFACTANT.