FR2652422A2 - PROCESS FOR PROCESSING A PHOTOGRAPHIC MEDIUM, MEANS USED AND MEDIUM THUS OBTAINED. - Google Patents

Abstract

Process for treatment of a photographic support comprising an image whitened after exposure, development and fixing in order to render said whitened image capable of being developed in daylight or in any other non-inactinic light, characterized by the fact that the photographic support comprising the whitened image is subjected, during a sufficient length of time, to the stabilising action of an acid bath containing an effective quantity of thiourea or equivalent blocking agent.

Description

 The purpose of this addition certificate is to improve the process in accordance with the main patent, for processing a photographic medium capable of allowing the development, in daylight or in the presence of any other non-inactinic light, of a bleached image comprising by said photographic medium.

 It also relates, and this as new industrial products, the means to be used in the context of the improvements made to the above process as well as the photographic support comprising the bleached image and subjected to the above processing process.

 It is recalled that a photographic support must be maintained, before and after exposure and until the final phase of development, namely the action of the fixer, protected from any non-inactinic light source.

 In fact, any exposure of said photographic support to a non-inactinic light source before or after exposure but before the application of the fixative results in the fact that the image to which the support has been exposed and which must appear and continue on the support after the well-known development and fixation treatment, is irreparably veiled.

 It was therefore impossible, before the invention which was the subject of the main patent, to reveal, that is to say to make appear in broad daylight on a photographic support constituted for example by a white sheet of photographic paper, an image correctly exposed before on the same medium.

 The inventors have had the merit of finding, as indicated in the main patent, that a conventionally whitened image, comprising a photographic support which is subjected after whitening of the image to the action of an acid bath having a effective content of thiourea or any other equivalent blocking agent, could be developed in broad daylight as well as in the presence of any other source of non-inactinic light by action on the support thus treated with a dilute alkaline solution.

 It follows that the method, in accordance with the main patent, of processing a photographic support comprising a bleached image after exposure, development and fixing in order to make the bleached image capable of being developed in daylight or in presence of any other non-inactinic light is characterized in that the photographic support comprising the bleached image is subjected, for a sufficient period, to the stabilizing action of an acid bath comprising an effective amount of thiourea or of an agent equivalent blocking agent, which may consist of sodium thiocyanate.

 The improvements brought by this certificate of addition reside in the fact that the acidity of the bath comprising an effective quantity of thiourea or of an equivalent blocking agent, is obtained by an effective quantity of oxalic acid.

 In practice, the effective amount of oxalic acid is 3.5 to 8 g, preferably 4.5 to 5.5 g per 1000 ml of bath.

 The acid bath thus formed, the pH of which is from 4.00 to 4.70, has a concentration of thiourea or any other equivalent blocking agent of between approximately 2 and approximately 3 g / l, this content preferably being close to 2.5 g / liter.

 To develop in daylight or in the presence of any other non-inactinic light a bleached image comprising a photographic support which has been subjected to the treatment in accordance with the invention, said photographic support is subjected to the action of a dilute alkaline solution.

 Thanks to the selection, in accordance with the present improvements, of oxalic acid to make the thiourea bath acidic, it becomes possible to omit the bisulfite treatment stage provided for according to the main patent between the bleaching stage and that of stabilization , which saves a lot of time.

 Proposing, therefore, to have a photographic medium include a bleached image capable of being developed in daylight as well as in the presence of any other non-inactinic light, it is done as follows or in a technically equivalent manner .

 First of all, an image is exposed, it is revealed and it is fixed by subjecting a photographic support to the conventional sequence of treatments well known to those skilled in the art, described in all photographic manuals and on which there n 'is therefore not necessary to insist here.

 Then, the photographic support is subjected to a treatment also known in itself and consisting in "whitening" the image previously revealed and fixed.

 To do this, a gelatin tanning is preferably carried out by causing an alum to act, for example, then the image is bleached by action, for example, potassium permanganate in an acid medium.

 Tanning and bleaching can be simultaneous and carried out by a single bath.

Advantageously, use may be made of a bath, the composition of which is given below by way of example:
potassium permanganate 7 g
sodium chloride 20 g
acetic acid (80% concentration) 60 ml
potassium alum 10 g
water qs 1000 ml.

 The photographic support comprising the image to be whitened can be immersed in the above bath, preferably at room temperature, until the image disappears; in practice, the duration of the action of the bath is approximately 4 minutes.

 The support comprising the image thus bleached is then subjected to the stabilization treatment process according to the invention.

 This treatment process can be applied immediately after bleaching and rinsing or later; in this second possibility, the support must be protected from light until the stabilization treatment.

 This stabilization treatment consists in subjecting the discolored photographic support which comprises the bleached image to the action, in an acid medium, of thiourea or of an equivalent blocking agent.

 The thiourea is used by means of a bath, the pH of which is brought to a value of 4.00 to 4.70, preferably close to 4.35, using the effective amount of acid oxalic specified above.

 The bath in question, the temperature of which is 18 to 22 ° C., preferably room temperature, preferably also contains a bromide to avoid the too rapid solubilization of the silver chloride and an alum to perfect the tanning of the gelatin. .

 It is applied to the photographic support to be treated for a period fixed between 90 and 120 seconds.

A bath which has led to good results and given by way of example has the following composition:
Thiourea 2.5 g
Oxalic acid 5 g
Potassium bromide 2 g
Potassium alum 50 g
Water qs 1000 ml.

 In the case of this particular bath, the duration of the treatment is approximately 105 seconds.

 In general, too high a concentration of thiourea and / or a too long treatment time inhibits redevelopment and gives a weakened image. Conversely, a concentration of thiourea that is too low and / or a treatment time that is too short insufficiently stabilizes the bleached image and does not prevent blackening in daylight.

 The treatment can be carried out by soaking the photographic support in this bath.

 It is followed by a sufficiently intense washing to remove from the support all the residues of the above-mentioned bath.

 After drying, the photographic support thus treated can be stored in daylight without limitation of duration and, as indicated in the main patent, it is made to act on said support, in daylight or in the presence of any other light not inactinque , an aqueous alkaline solution diluted to make the image reappear.

 The alkalinity can be advantageously provided by a 1% by weight solution of NaOH.

 Then proceed as indicated in the main patent.

Claims (9)

 1. Method for processing a photographic support comprising a bleached image after exposure, development and fixation in order to make said bleached image capable of being developed in daylight or in the presence of any other non-inactinic light, in which the photographic support comprising the bleached image is subjected, for a sufficient period, to the stabilizing action of an acid bath comprising an effective amount of thiourea or of an equivalent blocking agent, characterized in that the acidity of the bath comprising thiourea or equivalent blocking agent is supplied by an effective amount of oxalic acid.  2. Treatment method according to claim 1, characterized in that the pH of the acid bath is from 4.0 to 4.70, preferably close to 4.35.  3. Treatment method according to one of claims 1 and 2, characterized in that the effective amount of oxalic acid is 3.5 to 8.0 g, preferably 4.5 to 5.5 per 1000 ml of bath.  4. Treatment method according to one of claims 1 to 3, characterized in that the temperature of the acid bath is 18 to 22 C, preferably close to 200C and that the duration of action of the bath is 90 to 120 seconds, preferably close to 105 seconds.  5. Acid bath comprising a concentration of thiourea or equivalent blocking agent of between approximately 2 g / l and approximately 3 g / l, preferably close to 2.5 g / l, and intended to be used in the process according to one of claims 1 to 4, characterized in that it comprises an effective amount of 3.5 to 8.0 g, preferably 4.5 to 5.5 g / l of oxalic acid.  6. Bath according to claim 5, characterized in that its composition is as follows:  Thiourea 2.5 g  Oxalic acid 5 g  Potassium bromide 2 g  Potassium alum 50 g  Water q.s.p. 1000 ml.  7. Concentrate capable of supplying, by dilution with an appropriate quantity of water, the bath in accordance with one of claims 5 and 6.  8. Photographic support, characterized in that it includes a bleached image and that it has been subjected to the method according to one of claims 1 to 4.  9. A method of developing in broad daylight or in the presence of any other non-inactinic light of a bleached image comprised by a photographic support treated by a bath according to one of claims 5 and 6, characterized in that one subjects said photographic support to the action of a dilute alkaline solution.